Image encoding/decoding method and apparatus, and recording media storing bitstream

ABSTRACT

An image encoding/decoding method is provided. An image decoding method of the present invention may comprise constructing a motion information list for a current block, reconstructing a first index for a first triangular block within the current block and a second index for a second triangular block within the current block, and predicting the first triangular block and the second triangular block, based on the first index, the second index, and the motion information list.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding an image. Particularly, the present invention relatesto a method and apparatus for encoding/decoding an image based on splitblock prediction.

BACKGROUND ART

Recently, the demand for high resolution and quality images such as highdefinition (HD) or ultra-high definition (UHD) images has increased invarious applications. As the resolution and quality of images areimproved, the amount of data correspondingly increases. This is one ofthe causes of increase in transmission cost and storage cost whentransmitting image data through existing transmission media such aswired or wireless broadband channels or when storing image data. Inorder to solve such problems with high resolution and quality imagedata, a high efficiency image encoding/decoding technique is required.

There are various video compression techniques such as an interprediction technique of predicting the values of pixels within a currentpicture from the values of pixels within a preceding picture or asubsequent picture, an intra prediction technique of predicting thevalues of pixels within a region of a current picture from the values ofpixels within another region of the current picture, a transform andquantization technique of compressing the energy of a residual signal,and an entropy coding technique of allocating frequently occurring pixelvalues with shorter codes and less occurring pixel values with longercodes.

DISCLOSURE Technical Problem

An object of the present invention is to provide an imageencoding/decoding method and apparatus with improved encoding/decodingefficiency.

Another object of the present invention is to provide an imageencoding/decoding method and apparatus for performing split blockprediction effectively and signaling related information efficiently.

Another object of the present invention is to provide a recording mediumstoring a bitstream generated by an image encoding method/apparatus ofthe present invention.

Another object of the present invention is to provide a recording mediumstoring a bitstream which is received, decoded and used by an imagedecoding apparatus according to the present invention to reconstruct animage.

Technical Solution

An image decoding method according to an embodiment of the presentinvention may comprise constructing a motion information list for acurrent block, reconstructing a first index for a first triangular blockwithin the current block and a second index for a second triangularblock within the current block, and predicting the first triangularblock and the second triangular block, based on the first index, thesecond index, and the motion information list.

In the image decoding method of the present invention, the current blockis a quadrangle, and the first triangular block and the secondtriangular block may be regions that are generated by partitioning thecurrent block with a top left-bottom right diagonal or a topright-bottom left diagonal.

In the image decoding method of the present invention, information onwhether the current block is partitioned with the top left-bottom rightdiagonal or the top right-bottom left diagonal may be decoded from abitstream.

In the image decoding method of the present invention, the motioninformation list may comprise a predetermined number of pieces of motioninformation in an order of motion information of a spatially neighboringblock, motion information of a temporally neighboring block,buffer-based motion information, combination motion information, andzero motion information.

In the image decoding method of the present invention, the first indexand the second index may be different from each other.

In the image decoding method of the present invention, based on whetherthe first index or the second index is a predetermined index, aprediction direction of the first triangular block or the secondtriangular block may be determined.

In the image decoding method of the present invention, when the firstindex or the second index is an even number index, the predictiondirection of the first triangular block or the second triangular blockmay be an L0 direction, and when the first index or the second index isan odd number index, the prediction direction of the first triangularblock or the second triangular block may be an L1 direction.

In the image decoding method of the present invention, when motioninformation indicated by the first index or the second index does notinclude motion information in the determined prediction direction, thedetermined prediction direction may be changed into the oppositedirection.

In the image decoding method of the present invention, the method mayfurther comprise storing motion information within the current block ina 4×4 block unit.

In the image decoding method of the present invention, motioninformation of the second triangular block may be stored as motioninformation of a block corresponding to a boundary between the firsttriangular block and the second triangular block.

An image encoding method according to another embodiment of the presentinvention may comprise determining motion information for a firsttriangular block within a current block and motion information for asecond triangular block within the current block, predicting the firsttriangular block and the second triangular block, based on the motioninformation for the first triangular block and the motion informationfor the second triangular block, constructing a motion information listfor the current block, and encoding a first index for the firsttriangular block and a second index for the second triangular block,based on the motion information for the first triangular block, themotion information for the second triangular block and the motioninformation list.

In the image encoding method of the present invention, the current blockis a quadrangle, and the first triangular block and the secondtriangular block may be regions that are generated by partitioning thecurrent block with a top left-bottom right diagonal or a topright-bottom left diagonal.

In the image encoding method of the present invention, information onwhether the current block is partitioned with the top left-bottom rightdiagonal or the top right-bottom left diagonal may be encoded into abitstream.

In the image encoding method of the present invention, the motioninformation list may comprise a predetermined number of pieces of motioninformation in an order of motion information of a spatially neighboringblock, motion information of a temporally neighboring block,buffer-based motion information, combination motion information, andzero motion information.

In the image encoding method of the present invention, the first indexand the second index may be different from each other.

In the image encoding method of the present invention, based on whetherthe first index or the second index is a predetermined index, aprediction direction of the first triangular block or the secondtriangular block may be determined.

In the image encoding method of the present invention, when the firstindex or the second index is an even number index, the predictiondirection of the first triangular block or the second triangular blockmay be an L0 direction, and when the first index or the second index isan odd number index, the prediction direction of the first triangularblock or the second triangular block may be an L1 direction.

In the image encoding method of the present invention, when motioninformation indicated by the first index or the second index does notinclude motion information in the determined prediction direction, thedetermined prediction direction may be changed into the oppositedirection.

In the image encoding method of the present invention, the method mayfurther comprise storing motion information within the current block ina 4×4 block unit, and motion information of the second triangular blockmay be stored as motion information of a block corresponding to aboundary between the first triangular block and the second triangularblock.

A computer-readable recording medium according to another embodiment ofthe present invention may be a computer-readable recording mediumstoring a bitstream that is received, decoded and used to reconstruct animage by an image decoding apparatus, wherein the bitstream may comprisea first index for a first triangular block within a current block and asecond index for a second triangular block within the current block, thefirst index and the second index may be used with a motion informationlist for the current block to predict the first triangular block and thesecond triangular block.

A computer-readable recording medium according to another embodiment ofthe present invention may store a bitstream generated by an imageencoding method and/or apparatus according to the present invention.

Advantageous Effects

According to the present invention, an image encoding/decoding methodand apparatus with improved encoding/decoding efficiency may beprovided.

Also, according to the present invention, an image encoding/decodingmethod and apparatus for performing split block prediction effectivelyand signaling related information efficiently may be provided.

Also, according to the present invention, encoding complexity maydecrease when performing triangular split block prediction by reducingthe number of possible combinations of split direction to be searchedand motion information of each triangular split block.

Also, according to the present invention, calculation complexity maydecrease when storing motion information for a block corresponding to aboundary of two triangular splits because an additional process forgenerating bi-directional motion information is not needed.

Also, according to the present invention, a recording medium storing abitstream generated by an image encoding method/apparatus of the presentinvention may be provided.

Also, according to the present invention, a recording medium storing abitstream which is received, decoded and used by an image decodingapparatus according to the present invention to reconstruct an image maybe provided.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image.

FIG. 4 is a view showing an intra-prediction process.

FIG. 5 is a diagram illustrating an embodiment of an inter predictionprocess.

FIG. 6 is a diagram illustrating a transform and quantization process.

FIG. 7 is a diagram illustrating reference samples capable of being usedfor intra prediction.

FIG. 8 is a diagram illustrating an example of quadrangular symmetricpartitioning according to the present invention.

FIG. 9 is a diagram illustrating an example of quadrangular quadpartitioning according to the present invention.

FIG. 10 is a diagram illustrating an example of triangular symmetricpartitioning according to the present invention.

FIG. 11 is a diagram illustrating an example of triangular quadpartitioning according to the present invention.

FIG. 12 is a diagram illustrating an example of quadrangular asymmetricpartitioning according to the present invention.

FIG. 13 is a diagram illustrating another example of quadrangularasymmetric partitioning according to the present invention.

FIG. 14 is a diagram illustrating an example of triangular asymmetricpartitioning according to the present invention.

FIG. 15 is a diagram illustrating another example of triangularasymmetric partitioning according to the present invention.

FIG. 16 is a diagram illustrating an example of spatially neighboringblocks of the current block.

FIG. 17 is a diagram illustrating an example of temporally neighboringblocks of the current block.

FIG. 18 is a diagram illustrating prediction of split blocks accordingto the present invention.

FIG. 19 is a diagram illustrating an example of weighting factors basedon samples which are used for a weighted sum for prediction of splitblocks.

FIG. 20 is a diagram illustrating an example of boundary samples ofsplit blocks.

FIG. 21 is a diagram illustrating weighting factors applied to boundarysamples.

FIG. 22 is a diagram illustrating the basis of storage of motioninformation.

FIG. 23 is a diagram illustrating an example of split-block motioninformation storage according to the present invention.

FIG. 24 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 40.

FIG. 25 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 36.

FIG. 26 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 16.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, althoughthe exemplary embodiments can be construed as including allmodifications, equivalents, or substitutes in a technical concept and atechnical scope of the present invention. The similar reference numeralsrefer to the same or similar functions in various aspects. In thedrawings, the shapes and dimensions of elements may be exaggerated forclarity. In the following detailed description of the present invention,references are made to the accompanying drawings that show, by way ofillustration, specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to implement the present disclosure. Itshould be understood that various embodiments of the present disclosure,although different, are not necessarily mutually exclusive. For example,specific features, structures, and characteristics described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from the spirit and scope of the presentdisclosure. In addition, it should be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the spirit and scope of the presentdisclosure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present disclosure isdefined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to what the claims claim.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

Furthermore, constitutional parts shown in the embodiments of thepresent invention are independently shown so as to representcharacteristic functions different from each other. Thus, it does notmean that each constitutional part is constituted in a constitutionalunit of separated hardware or software. In other words, eachconstitutional part includes each of enumerated constitutional parts forconvenience. Thus, at least two constitutional parts of eachconstitutional part may be combined to form one constitutional part orone constitutional part may be divided into a plurality ofconstitutional parts to perform each function. The embodiment where eachconstitutional part is combined and the embodiment where oneconstitutional part is divided are also included in the scope of thepresent invention, if not departing from the essence of the presentinvention.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded. In other words, when a specific element is referred to as being“included”, elements other than the corresponding element are notexcluded, but additional elements may be included in embodiments of thepresent invention or the scope of the present invention.

In addition, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describingexemplary embodiments of the present invention, well-known functions orconstructions will not be described in detail since they mayunnecessarily obscure the understanding of the present invention. Thesame constituent elements in the drawings are denoted by the samereference numerals, and a repeated description of the same elements willbe omitted.

Hereinafter, an image may mean a picture configuring a video, or maymean the video itself. For example, “encoding or decoding or both of animage” may mean “encoding or decoding or both of a moving picture”, andmay mean “encoding or decoding or both of one image among images of amoving picture.”

Hereinafter, terms “moving picture” and “video” may be used as the samemeaning and be replaced with each other.

Hereinafter, a target image may be an encoding target image which is atarget of encoding and/or a decoding target image which is a target ofdecoding. Also, a target image may be an input image inputted to anencoding apparatus, and an input image inputted to a decoding apparatus.Here, a target image may have the same meaning with the current image.

Hereinafter, terms “image”, “picture, “frame” and “screen” may be usedas the same meaning and be replaced with each other.

Hereinafter, a target block may be an encoding target block which is atarget of encoding and/or a decoding target block which is a target ofdecoding. Also, a target block may be the current block which is atarget of current encoding and/or decoding. For example, terms “targetblock” and “current block” may be used as the same meaning and bereplaced with each other.

Hereinafter, terms “block” and “unit” may be used as the same meaningand be replaced with each other. Or a “block” may represent a specificunit.

Hereinafter, terms “region” and “segment” may be replaced with eachother.

Hereinafter, a specific signal may be a signal representing a specificblock. For example, an original signal may be a signal representing atarget block. A prediction signal may be a signal representing aprediction block. A residual signal may be a signal representing aresidual block.

In embodiments, each of specific information, data, flag, index, elementand attribute, etc. may have a value. A value of information, data,flag, index, element and attribute equal to “0” may represent a logicalfalse or the first predefined value. In other words, a value “0”, afalse, a logical false and the first predefined value may be replacedwith each other. A value of information, data, flag, index, element andattribute equal to “1” may represent a logical true or the secondpredefined value. In other words, a value “1”, a true, a logical trueand the second predefined value may be replaced with each other.

When a variable i or j is used for representing a column, a row or anindex, a value of i may be an integer equal to or greater than 0, orequal to or greater than 1. That is, the column, the row, the index,etc. may be counted from 0 or may be counted from 1.

Description of Terms

Encoder: means an apparatus performing encoding. That is, means anencoding apparatus.

Decoder: means an apparatus performing decoding. That is, means andecoding apparatus.

Block: is an M×N array of a sample. Herein, M and N may mean positiveintegers, and the block may mean a sample array of a two-dimensionalform. The block may refer to a unit. A current block my mean an encodingtarget block that becomes a target when encoding, or a decoding targetblock that becomes a target when decoding. In addition, the currentblock may be at least one of an encode block, a prediction block, aresidual block, and a transform block.

Sample: is a basic unit constituting a block. It may be expressed as avalue from 0 to 2^(Bd)−1 according to a bit depth (B_(d)). In thepresent invention, the sample may be used as a meaning of a pixel. Thatis, a sample, a pel, a pixel may have the same meaning with each other.

Unit: may refer to an encoding and decoding unit. When encoding anddecoding an image, the unit may be a region generated by partitioning asingle image. In addition, the unit may mean a subdivided unit when asingle image is partitioned into subdivided units during encoding ordecoding. That is, an image may be partitioned into a plurality ofunits. When encoding and decoding an image, a predetermined process foreach unit may be performed. A single unit may be partitioned intosub-units that have sizes smaller than the size of the unit. Dependingon functions, the unit may mean a block, a macroblock, a coding treeunit, a code tree block, a coding unit, a coding block), a predictionunit, a prediction block, a residual unit), a residual block, atransform unit, a transform block, etc. In addition, in order todistinguish a unit from a block, the unit may include a luma componentblock, a chroma component block associated with the luma componentblock, and a syntax element of each color component block. The unit mayhave various sizes and forms, and particularly, the form of the unit maybe a two-dimensional geometrical figure such as a square shape, arectangular shape, a trapezoid shape, a triangular shape, a pentagonalshape, etc. In addition, unit information may include at least one of aunit type indicating the coding unit, the prediction unit, the transformunit, etc., and a unit size, a unit depth, a sequence of encoding anddecoding of a unit, etc.

Coding Tree Unit: is configured with a single coding tree block of aluma component Y, and two coding tree blocks related to chromacomponents Cb and Cr. In addition, it may mean that including the blocksand a syntax element of each block. Each coding tree unit may bepartitioned by using at least one of a quad-tree partitioning method, abinary-tree partitioning method and ternary-tree partitioning method toconfigure a lower unit such as coding unit, prediction unit, transformunit, etc. It may be used as a term for designating a sample block thatbecomes a process unit when encoding/decoding an image as an inputimage. Here, the quad-tree may mean a quarternary-tree.

When the size of the coding block is within a predetermined range, thedivision is possible using only quad-tree partitioning. Here, thepredetermined range may be defined as at least one of a maximum size anda minimum size of a coding block in which the division is possible usingonly quad-tree partitioning. Information indicating a maximum/minimumsize of a coding block in which quad-tree partitioning is allowed may besignaled through a bitstream, and the information may be signaled in atleast one unit of a sequence, a picture parameter, a tile group, or aslice (segment). Alternatively, the maximum/minimum size of the codingblock may be a fixed size predetermined in the coder/decoder. Forexample, when the size of the coding block corresponds to 256×256 to64×64, the division is possible only using quad-tree partitioning.Alternatively, when the size of the coding block is larger than the sizeof the maximum conversion block, the division is possible only usingquad-tree partitioning. Herein, the block to be divided may be at leastone of a coding block and a transform block. In this case, informationindicating the division of the coded block (for example, split_flag) maybe a flag indicating whether or not to perform the quad-treepartitioning. When the size of the coding block falls within apredetermined range, the division is possible only using binary tree orternary tree partitioning. In this case, the above description of thequad-tree partitioning may be applied to binary tree partitioning orternary tree partitioning in the same manner.

Coding Tree Block: may be used as a term for designating any one of a Ycoding tree block, Cb coding tree block, and Cr coding tree block.

Neighbor Block: may mean a block adjacent to a current block. The blockadjacent to the current block may mean a block that comes into contactwith a boundary of the current block, or a block positioned within apredetermined distance from the current block. The neighbor block maymean a block adjacent to a vertex of the current block. Herein, theblock adjacent to the vertex of the current block may mean a blockvertically adjacent to a neighbor block that is horizontally adjacent tothe current block, or a block horizontally adjacent to a neighbor blockthat is vertically adjacent to the current block.

Reconstructed Neighbor block: may mean a neighbor block adjacent to acurrent block and which has been already spatially/temporally encoded ordecoded. Herein, the reconstructed neighbor block may mean areconstructed neighbor unit. A reconstructed spatial neighbor block maybe a block within a current picture and which has been alreadyreconstructed through encoding or decoding or both. A reconstructedtemporal neighbor block is a block at a corresponding position as thecurrent block of the current picture within a reference image, or aneighbor block thereof.

Unit Depth: may mean a partitioned degree of a unit. In a treestructure, the highest node(Root Node) may correspond to the first unitwhich is not partitioned. Also, the highest node may have the leastdepth value. In this case, the highest node may have a depth of level 0.A node having a depth of level 1 may represent a unit generated bypartitioning once the first unit. A node having a depth of level 2 mayrepresent a unit generated by partitioning twice the first unit. A nodehaving a depth of level n may represent a unit generated by partitioningn-times the first unit. A Leaf Node may be the lowest node and a nodewhich cannot be partitioned further. A depth of a Leaf Node may be themaximum level. For example, a predefined value of the maximum level maybe 3. A depth of a root node may be the lowest and a depth of a leafnode may be the deepest. In addition, when a unit is expressed as a treestructure, a level in which a unit is present may mean a unit depth.

Bitstream: may mean a bitstream including encoding image information.

Parameter Set: corresponds to header information among a configurationwithin a bitstream. At least one of a video parameter set, a sequenceparameter set, a picture parameter set, and an adaptation parameter setmay be included in a parameter set. In addition, a parameter set mayinclude a slice header, a tile group header, and tile headerinformation. The term “tile group” means a group of tiles and has thesame meaning as a slice.

An adaptation parameter set may mean a parameter set that can be sharedby being referred to in different pictures, subpictures, slices, tilegroups, tiles, or bricks. In addition, information in an adaptationparameter set may be used by referring to different adaptation parametersets for a subpicture, a slice, a tile group, a tile, or a brick insidea picture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a subpicture, a slice, a tilegroup, a tile, or a brick inside a picture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a slice, a tile group, a tile,or a brick inside a subpicture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a tile or a brick inside aslice.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a brick inside a tile.

Information on an adaptation parameter set identifier may be included ina parameter set or a header of the subpicture, and an adaptationparameter set corresponding to the adaptation parameter set identifiermay be used for the subpicture.

The information on the adaptation parameter set identifier may beincluded in a parameter set or a header of the tile, and an adaptationparameter set corresponding to the adaptation parameter set identifiermay be used for the tile.

The information on the adaptation parameter set identifier may beincluded in a header of the brick, and an adaptation parameter setcorresponding to the adaptation parameter set identifier may be used forthe brick.

The picture may be partitioned into one or more tile rows and one ormore tile columns.

The subpicture may be partitioned into one or more tile rows and one ormore tile columns within a picture. The subpicture may be a regionhaving the form of a rectangle/square within a picture and may includeone or more CTUs. In addition, at least one or more tiles/bricks/slicesmay be included within one subpicture.

The tile may be a region having the form of a rectangle/square within apicture and may include one or more CTUs. In addition, the tile may bepartitioned into one or more bricks.

The brick may mean one or more CTU rows within a tile. The tile may bepartitioned into one or more bricks, and each brick may have at leastone or more CTU rows. A tile that is not partitioned into two or moremay mean a brick.

The slice may include one or more tiles within a picture and may includeone or more bricks within a tile.

Parsing: may mean determination of a value of a syntax element byperforming entropy decoding, or may mean the entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter,and a transform coefficient value of an encoding/decoding target unit.In addition, the symbol may mean an entropy encoding target or anentropy decoding result.

Prediction Mode: may be information indicating a mode encoded/decodedwith intra prediction or a mode encoded/decoded with inter prediction.

Prediction Unit: may mean a basic unit when performing prediction suchas inter-prediction, intra-prediction, inter-compensation,intra-compensation, and motion compensation. A single prediction unitmay be partitioned into a plurality of partitions having a smaller size,or may be partitioned into a plurality of lower prediction units. Aplurality of partitions may be a basic unit in performing prediction orcompensation. A partition which is generated by dividing a predictionunit may also be a prediction unit.

Prediction Unit Partition: may mean a form obtained by partitioning aprediction unit.

Reference picture list may refer to a list including one or morereference pictures used for inter prediction or motion compensation.There are several types of usable reference picture lists, including LC(List combined), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

Inter prediction indicator may refer to a direction of inter prediction(unidirectional prediction, bidirectional prediction, etc.) of a currentblock. Alternatively, it may refer to the number of reference picturesused to generate a prediction block of a current block. Alternatively,it may refer to the number of prediction blocks used at the time ofperforming inter prediction or motion compensation on a current block.

Prediction list utilization flag indicates whether a prediction block isgenerated using at least one reference picture in a specific referencepicture list. An inter prediction indicator can be derived using aprediction list utilization flag, and conversely, a prediction listutilization flag can be derived using an inter prediction indicator. Forexample, when the prediction list utilization flag has a first value ofzero (0), it means that a reference picture in a reference picture listis not used to generate a prediction block. On the other hand, when theprediction list utilization flag has a second value of one (1), it meansthat a reference picture list is used to generate a prediction block.

Reference picture index may refer to an index indicating a specificreference picture in a reference picture list.

Reference picture may mean a reference picture which is referred to by aspecific block for the purposes of inter prediction or motioncompensation of the specific block. Alternatively, the reference picturemay be a picture including a reference block referred to by a currentblock for inter prediction or motion compensation. Hereinafter, theterms “reference picture” and “reference image” have the same meaningand can be interchangeably.

Motion vector may be a two-dimensional vector used for inter predictionor motion compensation. The motion vector may mean an offset between anencoding/decoding target block and a reference block. For example, (mvX,mvY) may represent a motion vector. Here, mvX may represent a horizontalcomponent and mvY may represent a vertical component.

Search range may be a two-dimensional region which is searched toretrieve a motion vector during inter prediction. For example, the sizeof the search range may be M×N. Here, M and N are both integers.

Motion vector candidate may refer to a prediction candidate block or amotion vector of the prediction candidate block when predicting a motionvector. In addition, a motion vector candidate may be included in amotion vector candidate list.

Motion vector candidate list may mean a list composed of one or moremotion vector candidates.

Motion vector candidate index may mean an indicator indicating a motionvector candidate in a motion vector candidate list. Alternatively, itmay be an index of a motion vector predictor.

Motion information may mean information including at least one of theitems including a motion vector, a reference picture index, an interprediction indicator, a prediction list utilization flag, referencepicture list information, a reference picture, a motion vectorcandidate, a motion vector candidate index, a merge candidate, and amerge index.

Merge candidate list may mean a list composed of one or more mergecandidates.

Merge candidate may mean a spatial merge candidate, a temporal mergecandidate, a combined merge candidate, a combined bi-predictive mergecandidate, or a zero merge candidate. The merge candidate may includemotion information such as a reference picture index for each list, amotion vector, a prediction list utilization flag, and an interprediction indicator.

Merge index may mean an indicator indicating a merge candidate in amerge candidate list. Alternatively, the merge index may indicate ablock from which a merge candidate has been derived, among reconstructedblocks spatially/temporally adjacent to a current block. Alternatively,the merge index may indicate at least one piece of motion information ofa merge candidate.

Transform Unit: may mean a basic unit when performing encoding/decodingsuch as transform, inverse-transform, quantization, dequantization,transform coefficient encoding/decoding of a residual signal. A singletransform unit may be partitioned into a plurality of lower-leveltransform units having a smaller size. Here,transformation/inverse-transformation may comprise at least one amongthe first transformation/the first inverse-transformation and the secondtransformation/the second inverse-transformation.

Scaling: may mean a process of multiplying a quantized level by afactor. A transform coefficient may be generated by scaling a quantizedlevel. The scaling also may be referred to as dequantization.

Quantization Parameter: may mean a value used when generating aquantized level using a transform coefficient during quantization. Thequantization parameter also may mean a value used when generating atransform coefficient by scaling a quantized level duringdequantization. The quantization parameter may be a value mapped on aquantization step size.

Delta Quantization Parameter: may mean a difference value between apredicted quantization parameter and a quantization parameter of anencoding/decoding target unit.

Scan: may mean a method of sequencing coefficients within a unit, ablock or a matrix. For example, changing a two-dimensional matrix ofcoefficients into a one-dimensional matrix may be referred to asscanning, and changing a one-dimensional matrix of coefficients into atwo-dimensional matrix may be referred to as scanning or inversescanning.

Transform Coefficient: may mean a coefficient value generated aftertransform is performed in an encoder. It may mean a coefficient valuegenerated after at least one of entropy decoding and dequantization isperformed in a decoder. A quantized level obtained by quantizing atransform coefficient or a residual signal, or a quantized transformcoefficient level also may fall within the meaning of the transformcoefficient.

Quantized Level: may mean a value generated by quantizing a transformcoefficient or a residual signal in an encoder. Alternatively, thequantized level may mean a value that is a dequantization target toundergo dequantization in a decoder. Similarly, a quantized transformcoefficient level that is a result of transform and quantization alsomay fall within the meaning of the quantized level.

Non-zero Transform Coefficient: may mean a transform coefficient havinga value other than zero, or a transform coefficient level or a quantizedlevel having a value other than zero.

Quantization Matrix: may mean a matrix used in a quantization process ora dequantization process performed to improve subjective or objectiveimage quality. The quantization matrix also may be referred to as ascaling list.

Quantization Matrix Coefficient: may mean each element within aquantization matrix. The quantization matrix coefficient also may bereferred to as a matrix coefficient.

Default Matrix: may mean a predetermined quantization matrixpreliminarily defined in an encoder or a decoder.

Non-default Matrix: may mean a quantization matrix that is notpreliminarily defined in an encoder or a decoder but is signaled by auser.

Statistic Value: a statistic value for at least one among a variable, anencoding parameter, a constant value, etc. which have a computablespecific value may be one or more among an average value, a sum value, aweighted average value, a weighted sum value, the minimum value, themaximum value, the most frequent value, a median value, an interpolatedvalue of the corresponding specific values.

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

An encoding apparatus 100 may be an encoder, a video encoding apparatus,or an image encoding apparatus. A video may include at least one image.The encoding apparatus 100 may sequentially encode at least one image.

Referring to FIG. 1, the encoding apparatus 100 may include a motionprediction unit 111, a motion compensation unit 112, an intra-predictionunit 120, a switch 115, a subtractor 125, a transform unit 130, aquantization unit 140, an entropy encoding unit 150, a dequantizationunit 160, an inverse-transform unit 170, an adder 175, a filter unit180, and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding of an input image byusing an intra mode or an inter mode or both. In addition, encodingapparatus 100 may generate a bitstream including encoded informationthrough encoding the input image, and output the generated bitstream.The generated bitstream may be stored in a computer readable recordingmedium, or may be streamed through a wired/wireless transmission medium.When an intra mode is used as a prediction mode, the switch 115 may beswitched to an intra. Alternatively, when an inter mode is used as aprediction mode, the switch 115 may be switched to an inter mode.Herein, the intra mode may mean an intra-prediction mode, and the intermode may mean an inter-prediction mode. The encoding apparatus 100 maygenerate a prediction block for an input block of the input image. Inaddition, the encoding apparatus 100 may encode a residual block using aresidual of the input block and the prediction block after theprediction block being generated. The input image may be called as acurrent image that is a current encoding target. The input block may becalled as a current block that is current encoding target, or as anencoding target block.

When a prediction mode is an intra mode, the intra-prediction unit 120may use a sample of a block that has been already encoded/decoded and isadjacent to a current block as a reference sample. The intra-predictionunit 120 may perform spatial prediction for the current block by using areference sample, or generate prediction samples of an input block byperforming spatial prediction. Herein, the intra prediction may meanintra-prediction.

When a prediction mode is an inter mode, the motion prediction unit 111may retrieve a region that best matches with an input block from areference image when performing motion prediction, and deduce a motionvector by using the retrieved region. In this case, a search region maybe used as the region. The reference image may be stored in thereference picture buffer 190. Here, when encoding/decoding for thereference image is performed, it may be stored in the reference picturebuffer 190.

The motion compensation unit 112 may generate a prediction block byperforming motion compensation for the current block using a motionvector. Herein, inter-prediction may mean inter-prediction or motioncompensation.

When the value of the motion vector is not an integer, the motionprediction unit 111 and the motion compensation unit 112 may generatethe prediction block by applying an interpolation filter to a partialregion of the reference picture. In order to perform inter prediction ormotion compensation on a coding unit, it may be determined that whichmode among a skip mode, a merge mode, an advanced motion vectorprediction (AMVP) mode, and a current picture referring mode is used formotion prediction and motion compensation of a prediction unit includedin the corresponding coding unit. Then, inter prediction or motioncompensation may be differently performed depending on the determinedmode.

The subtractor 125 may generate a residual block by using a differenceof an input block and a prediction block. The residual block may becalled as a residual signal. The residual signal may mean a differencebetween an original signal and a prediction signal. In addition, theresidual signal may be a signal generated by transforming or quantizing,or transforming and quantizing a difference between the original signaland the prediction signal. The residual block may be a residual signalof a block unit.

The transform unit 130 may generate a transform coefficient byperforming transform of a residual block, and output the generatedtransform coefficient. Herein, the transform coefficient may be acoefficient value generated by performing transform of the residualblock. When a transform skip mode is applied, the transform unit 130 mayskip transform of the residual block.

A quantized level may be generated by applying quantization to thetransform coefficient or to the residual signal. Hereinafter, thequantized level may be also called as a transform coefficient inembodiments.

The quantization unit 140 may generate a quantized level by quantizingthe transform coefficient or the residual signal according to aparameter, and output the generated quantized level. Herein, thequantization unit 140 may quantize the transform coefficient by using aquantization matrix.

The entropy encoding unit 150 may generate a bitstream by performingentropy encoding according to a probability distribution on valuescalculated by the quantization unit 140 or on coding parameter valuescalculated when performing encoding, and output the generated bitstream.The entropy encoding unit 150 may perform entropy encoding of sampleinformation of an image and information for decoding an image. Forexample, the information for decoding the image may include a syntaxelement.

When entropy encoding is applied, symbols are represented so that asmaller number of bits are assigned to a symbol having a high chance ofbeing generated and a larger number of bits are assigned to a symbolhaving a low chance of being generated, and thus, the size of bit streamfor symbols to be encoded may be decreased. The entropy encoding unit150 may use an encoding method for entropy encoding such as exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), etc. For example, theentropy encoding unit 150 may perform entropy encoding by using avariable length coding/code (VLC) table. In addition, the entropyencoding unit 150 may deduce a binarization method of a target symboland a probability model of a target symbol/bin, and perform arithmeticcoding by using the deduced binarization method, and a context model.

In order to encode a transform coefficient level (quantized level), theentropy encoding unit 150 may change a two-dimensional block formcoefficient into a one-dimensional vector form by using a transformcoefficient scanning method.

A coding parameter may include information (flag, index, etc.) such assyntax element that is encoded in an encoder and signaled to a decoder,and information derived when performing encoding or decoding. The codingparameter may mean information required when encoding or decoding animage. For example, at least one value or a combination form of aunit/block size, a unit/block depth, unit/block partition information,unit/block shape, unit/block partition structure, whether to partitionof a quad-tree form, whether to partition of a binary-tree form, apartition direction of a binary-tree form (horizontal direction orvertical direction), a partition form of a binary-tree form (symmetricpartition or asymmetric partition), whether or not a current coding unitis partitioned by ternary tree partitioning, direction (horizontal orvertical direction) of the ternary tree partitioning, type (symmetric orasymmetric type) of the ternary tree partitioning, whether a currentcoding unit is partitioned by multi-type tree partitioning, direction(horizontal or vertical direction) of the multi-type three partitioning,type (symmetric or asymmetric type) of the multi-type tree partitioning,and a tree (binary tree or ternary tree) structure of the multi-typetree partitioning, a prediction mode (intra prediction or interprediction), a luma intra-prediction mode/direction, a chromaintra-prediction mode/direction, intra partition information, interpartition information, a coding block partition flag, a prediction blockpartition flag, a transform block partition flag, a reference samplefiltering method, a reference sample filter tab, a reference samplefilter coefficient, a prediction block filtering method, a predictionblock filter tap, a prediction block filter coefficient, a predictionblock boundary filtering method, a prediction block boundary filter tab,a prediction block boundary filter coefficient, an intra-predictionmode, an inter-prediction mode, motion information, a motion vector, amotion vector difference, a reference picture index, a inter-predictionangle, an inter-prediction indicator, a prediction list utilizationflag, a reference picture list, a reference picture, a motion vectorpredictor index, a motion vector predictor candidate, a motion vectorcandidate list, whether to use a merge mode, a merge index, a mergecandidate, a merge candidate list, whether to use a skip mode, aninterpolation filter type, an interpolation filter tab, an interpolationfilter coefficient, a motion vector size, a presentation accuracy of amotion vector, a transform type, a transform size, information ofwhether or not a primary (first) transform is used, information ofwhether or not a secondary transform is used, a primary transform index,a secondary transform index, information of whether or not a residualsignal is present, a coded block pattern, a coded block flag (CBF), aquantization parameter, a quantization parameter residue, a quantizationmatrix, whether to apply an intra loop filter, an intra loop filtercoefficient, an intra loop filter tab, an intra loop filter shape/form,whether to apply a deblocking filter, a deblocking filter coefficient, adeblocking filter tab, a deblocking filter strength, a deblocking filtershape/form, whether to apply an adaptive sample offset, an adaptivesample offset value, an adaptive sample offset category, an adaptivesample offset type, whether to apply an adaptive loop filter, anadaptive loop filter coefficient, an adaptive loop filter tab, anadaptive loop filter shape/form, a binarization/inverse-binarizationmethod, a context model determining method, a context model updatingmethod, whether to perform a regular mode, whether to perform a bypassmode, a context bin, a bypass bin, a significant coefficient flag, alast significant coefficient flag, a coded flag for a unit of acoefficient group, a position of the last significant coefficient, aflag for whether a value of a coefficient is larger than 1, a flag forwhether a value of a coefficient is larger than 2, a flag for whether avalue of a coefficient is larger than 3, information on a remainingcoefficient value, a sign information, a reconstructed luma sample, areconstructed chroma sample, a residual luma sample, a residual chromasample, a luma transform coefficient, a chroma transform coefficient, aquantized luma level, a quantized chroma level, a transform coefficientlevel scanning method, a size of a motion vector search area at adecoder side, a shape of a motion vector search area at a decoder side,a number of time of a motion vector search at a decoder side,information on a CTU size, information on a minimum block size,information on a maximum block size, information on a maximum blockdepth, information on a minimum block depth, an imagedisplaying/outputting sequence, slice identification information, aslice type, slice partition information, tile identificationinformation, a tile type, tile partition information, tile groupidentification information, a tile group type, tile group partitioninformation, a picture type, a bit depth of an input sample, a bit depthof a reconstruction sample, a bit depth of a residual sample, a bitdepth of a transform coefficient, a bit depth of a quantized level, andinformation on a luma signal or information on a chroma signal may beincluded in the coding parameter.

Herein, signaling the flag or index may mean that a corresponding flagor index is entropy encoded and included in a bitstream by an encoder,and may mean that the corresponding flag or index is entropy decodedfrom a bitstream by a decoder.

When the encoding apparatus 100 performs encoding throughinter-prediction, an encoded current image may be used as a referenceimage for another image that is processed afterwards. Accordingly, theencoding apparatus 100 may reconstruct or decode the encoded currentimage, or store the reconstructed or decoded image as a reference imagein reference picture buffer 190.

A quantized level may be dequantized in the dequantization unit 160, ormay be inverse-transformed in the inverse-transform unit 170. Adequantized or inverse-transformed coefficient or both may be added witha prediction block by the adder 175. By adding the dequantized orinverse-transformed coefficient or both with the prediction block, areconstructed block may be generated. Herein, the dequantized orinverse-transformed coefficient or both may mean a coefficient on whichat least one of dequantization and inverse-transform is performed, andmay mean a reconstructed residual block.

A reconstructed block may pass through the filter unit 180. The filterunit 180 may apply at least one of a deblocking filter, a sampleadaptive offset (SAO), and an adaptive loop filter (ALF) to areconstructed sample, a reconstructed block or a reconstructed image.The filter unit 180 may be called as an in-loop filter.

The deblocking filter may remove block distortion generated inboundaries between blocks. In order to determine whether or not to applya deblocking filter, whether or not to apply a deblocking filter to acurrent block may be determined based samples included in several rowsor columns which are included in the block. When a deblocking filter isapplied to a block, another filter may be applied according to arequired deblocking filtering strength.

In order to compensate an encoding error, a proper offset value may beadded to a sample value by using a sample adaptive offset. The sampleadaptive offset may correct an offset of a deblocked image from anoriginal image by a sample unit. A method of partitioning samples of animage into a predetermined number of regions, determining a region towhich an offset is applied, and applying the offset to the determinedregion, or a method of applying an offset in consideration of edgeinformation on each sample may be used.

The adaptive loop filter may perform filtering based on a comparisonresult of the filtered reconstructed image and the original image.Samples included in an image may be partitioned into predeterminedgroups, a filter to be applied to each group may be determined, anddifferential filtering may be performed for each group. Information ofwhether or not to apply the ALF may be signaled by coding units (CUs),and a form and coefficient of the ALF to be applied to each block mayvary.

The reconstructed block or the reconstructed image having passed throughthe filter unit 180 may be stored in the reference picture buffer 190. Areconstructed block processed by the filter unit 180 may be a part of areference image. That is, a reference image is a reconstructed imagecomposed of reconstructed blocks processed by the filter unit 180. Thestored reference image may be used later in inter prediction or motioncompensation.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

A decoding apparatus 200 may a decoder, a video decoding apparatus, oran image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a dequantization unit 220, an inverse-transform unit230, an intra-prediction unit 240, a motion compensation unit 250, anadder 225, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from theencoding apparatus 100. The decoding apparatus 200 may receive abitstream stored in a computer readable recording medium, or may receivea bitstream that is streamed through a wired/wireless transmissionmedium. The decoding apparatus 200 may decode the bitstream by using anintra mode or an inter mode. In addition, the decoding apparatus 200 maygenerate a reconstructed image generated through decoding or a decodedimage, and output the reconstructed image or decoded image.

When a prediction mode used when decoding is an intra mode, a switch maybe switched to an intra. Alternatively, when a prediction mode used whendecoding is an inter mode, a switch may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block bydecoding the input bitstream, and generate a prediction block. When thereconstructed residual block and the prediction block are obtained, thedecoding apparatus 200 may generate a reconstructed block that becomes adecoding target by adding the reconstructed residual block with theprediction block. The decoding target block may be called a currentblock.

The entropy decoding unit 210 may generate symbols by entropy decodingthe bitstream according to a probability distribution. The generatedsymbols may include a symbol of a quantized level form. Herein, anentropy decoding method may be a inverse-process of the entropy encodingmethod described above.

In order to decode a transform coefficient level (quantized level), theentropy decoding unit 210 may change a one-directional vector formcoefficient into a two-dimensional block form by using a transformcoefficient scanning method.

A quantized level may be dequantized in the dequantization unit 220, orinverse-transformed in the inverse-transform unit 230. The quantizedlevel may be a result of dequantizing or inverse-transforming or both,and may be generated as a reconstructed residual block. Herein, thedequantization unit 220 may apply a quantization matrix to the quantizedlevel.

When an intra mode is used, the intra-prediction unit 240 may generate aprediction block by performing, for the current block, spatialprediction that uses a sample value of a block adjacent to a decodingtarget block and which has been already decoded.

When an inter mode is used, the motion compensation unit 250 maygenerate a prediction block by performing, for the current block, motioncompensation that uses a motion vector and a reference image stored inthe reference picture buffer 270.

The adder 225 may generate a reconstructed block by adding thereconstructed residual block with the prediction block. The filter unit260 may apply at least one of a deblocking filter, a sample adaptiveoffset, and an adaptive loop filter to the reconstructed block orreconstructed image. The filter unit 260 may output the reconstructedimage. The reconstructed block or reconstructed image may be stored inthe reference picture buffer 270 and used when performinginter-prediction. A reconstructed block processed by the filter unit 260may be a part of a reference image. That is, a reference image is areconstructed image composed of reconstructed blocks processed by thefilter unit 260. The stored reference image may be used later in interprediction or motion compensation.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image. FIG. 3 schematically shows anexample of partitioning a single unit into a plurality of lower units.

In order to efficiently partition an image, when encoding and decoding,a coding unit (CU) may be used. The coding unit may be used as a basicunit when encoding/decoding the image. In addition, the coding unit maybe used as a unit for distinguishing an intra prediction mode and aninter prediction mode when encoding/decoding the image. The coding unitmay be a basic unit used for prediction, transform, quantization,inverse-transform, dequantization, or an encoding/decoding process of atransform coefficient.

Referring to FIG. 3, an image 300 is sequentially partitioned in alargest coding unit (LCU), and a LCU unit is determined as a partitionstructure. Herein, the LCU may be used in the same meaning as a codingtree unit (CTU). A unit partitioning may mean partitioning a blockassociated with to the unit. In block partition information, informationof a unit depth may be included. Depth information may represent anumber of times or a degree or both in which a unit is partitioned. Asingle unit may be partitioned into a plurality of lower level unitshierarchically associated with depth information based on a treestructure. In other words, a unit and a lower level unit generated bypartitioning the unit may correspond to a node and a child node of thenode, respectively. Each of partitioned lower unit may have depthinformation. Depth information may be information representing a size ofa CU, and may be stored in each CU. Unit depth represents times and/ordegrees related to partitioning a unit. Therefore, partitioninginformation of a lower-level unit may comprise information on a size ofthe lower-level unit.

A partition structure may mean a distribution of a coding unit (CU)within an LCU 310. Such a distribution may be determined according towhether or not to partition a single CU into a plurality (positiveinteger equal to or greater than 2 including 2, 4, 8, 16, etc.) of CUs.A horizontal size and a vertical size of the CU generated bypartitioning may respectively be half of a horizontal size and avertical size of the CU before partitioning, or may respectively havesizes smaller than a horizontal size and a vertical size beforepartitioning according to a number of times of partitioning. The CU maybe recursively partitioned into a plurality of CUs. By the recursivepartitioning, at least one among a height and a width of a CU afterpartitioning may decrease comparing with at least one among a height anda width of a CU before partitioning. Partitioning of the CU may berecursively performed until to a predefined depth or predefined size.For example, a depth of an LCU may be 0, and a depth of a smallestcoding unit (SCU) may be a predefined maximum depth. Herein, the LCU maybe a coding unit having a maximum coding unit size, and the SCU may be acoding unit having a minimum coding unit size as described above.Partitioning is started from the LCU 310, a CU depth increases by 1 as ahorizontal size or a vertical size or both of the CU decreases bypartitioning. For example, for each depth, a CU which is not partitionedmay have a size of 2N×2N. Also, in case of a CU which is partitioned, aCU with a size of 2N×2N may be partitioned into four CUs with a size ofN×N. A size of N may decrease to half as a depth increase by 1.

In addition, information whether or not the CU is partitioned may berepresented by using partition information of the CU. The partitioninformation may be 1-bit information. All CUs, except for a SCU, mayinclude partition information. For example, when a value of partitioninformation is a first value, the CU may not be partitioned, when avalue of partition information is a second value, the CU may bepartitioned

Referring to FIG. 3, an LCU having a depth 0 may be a 64×64 block. 0 maybe a minimum depth. A SCU having a depth 3 may be an 8×8 block. 3 may bea maximum depth. A CU of a 32×32 block and a 16×16 block may berespectively represented as a depth 1 and a depth 2.

For example, when a single coding unit is partitioned into four codingunits, a horizontal size and a vertical size of the four partitionedcoding units may be a half size of a horizontal and vertical size of theCU before being partitioned. In one embodiment, when a coding unithaving a 32×32 size is partitioned into four coding units, each of thefour partitioned coding units may have a 16×16 size. When a singlecoding unit is partitioned into four coding units, it may be called thatthe coding unit may be partitioned into a quad-tree form.

For example, when one coding unit is partitioned into two sub-codingunits, the horizontal or vertical size (width or height) of each of thetwo sub-coding units may be half the horizontal or vertical size of theoriginal coding unit. For example, when a coding unit having a size of32×32 is vertically partitioned into two sub-coding units, each of thetwo sub-coding units may have a size of 16×32. For example, when acoding unit having a size of 8×32 is horizontally partitioned into twosub-coding units, each of the two sub-coding units may have a size of8×16. When one coding unit is partitioned into two sub-coding units, itcan be said that the coding unit is binary-partitioned or is partitionedby a binary tree partition structure.

For example, when one coding unit is partitioned into three sub-codingunits, the horizontal or vertical size of the coding unit can bepartitioned with a ratio of 1:2:1, thereby producing three sub-codingunits whose horizontal or vertical sizes are in a ratio of 1:2:1. Forexample, when a coding unit having a size of 16×32 is horizontallypartitioned into three sub-coding units, the three sub-coding units mayhave sizes of 16×8, 16×16, and 16×8 respectively, in the order from theuppermost to the lowermost sub-coding unit. For example, when a codingunit having a size of 32×32 is vertically split into three sub-codingunits, the three sub-coding units may have sizes of 8×32, 16×32, and8×32, respectively in the order from the left to the right sub-codingunit. When one coding unit is partitioned into three sub-coding units,it can be said that the coding unit is ternary-partitioned orpartitioned by a ternary tree partition structure.

In FIG. 3, a coding tree unit (CTU) 320 is an example of a CTU to whicha quad tree partition structure, a binary tree partition structure, anda ternary tree partition structure are all applied.

As described above, in order to partition the CTU, at least one of aquad tree partition structure, a binary tree partition structure, and aternary tree partition structure may be applied. Various tree partitionstructures may be sequentially applied to the CTU, according to apredetermined priority order. For example, the quad tree partitionstructure may be preferentially applied to the CTU. A coding unit thatcannot be partitioned any longer using a quad tree partition structuremay correspond to a leaf node of a quad tree. A coding unitcorresponding to a leaf node of a quad tree may serve as a root node ofa binary and/or ternary tree partition structure. That is, a coding unitcorresponding to a leaf node of a quad tree may be further partitionedby a binary tree partition structure or a ternary tree partitionstructure, or may not be further partitioned. Therefore, by preventing acoding block that results from binary tree partitioning or ternary treepartitioning of a coding unit corresponding to a leaf node of a quadtree from undergoing further quad tree partitioning, block partitioningand/or signaling of partition information can be effectively performed.

The fact that a coding unit corresponding to a node of a quad tree ispartitioned may be signaled using quad partition information. The quadpartition information having a first value (e.g., “1”) may indicate thata current coding unit is partitioned by the quad tree partitionstructure. The quad partition information having a second value (e.g.,“0”) may indicate that a current coding unit is not partitioned by thequad tree partition structure. The quad partition information may be aflag having a predetermined length (e.g., one bit).

There may not be a priority between the binary tree partitioning and theternary tree partitioning. That is, a coding unit corresponding to aleaf node of a quad tree may further undergo arbitrary partitioningamong the binary tree partitioning and the ternary tree partitioning. Inaddition, a coding unit generated through the binary tree partitioningor the ternary tree partitioning may undergo a further binary treepartitioning or a further ternary tree partitioning, or may not befurther partitioned.

A tree structure in which there is no priority among the binary treepartitioning and the ternary tree partitioning is referred to as amulti-type tree structure. A coding unit corresponding to a leaf node ofa quad tree may serve as a root node of a multi-type tree. Whether topartition a coding unit which corresponds to a node of a multi-type treemay be signaled using at least one of multi-type tree partitionindication information, partition direction information, and partitiontree information. For partitioning of a coding unit corresponding to anode of a multi-type tree, the multi-type tree partition indicationinformation, the partition direction information, and the partition treeinformation may be sequentially signaled.

The multi-type tree partition indication information having a firstvalue (e.g., “1”) may indicate that a current coding unit is to undergoa multi-type tree partitioning. The multi-type tree partition indicationinformation having a second value (e.g., “0”) may indicate that acurrent coding unit is not to undergo a multi-type tree partitioning.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, the codingunit may include partition direction information. The partitiondirection information may indicate in which direction a current codingunit is to be partitioned for the multi-type tree partitioning. Thepartition direction information having a first value (e.g., “1”) mayindicate that a current coding unit is to be vertically partitioned. Thepartition direction information having a second value (e.g., “0”) mayindicate that a current coding unit is to be horizontally partitioned.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, thecurrent coding unit may include partition tree information. Thepartition tree information may indicate a tree partition structure whichis to be used for partitioning of a node of a multi-type tree. Thepartition tree information having a first value (e.g., “1”) may indicatethat a current coding unit is to be partitioned by a binary treepartition structure. The partition tree information having a secondvalue (e.g., “0”) may indicate that a current coding unit is to bepartitioned by a ternary tree partition structure.

The partition indication information, the partition tree information,and the partition direction information may each be a flag having apredetermined length (e.g., one bit).

At least any one of the quadtree partition indication information, themulti-type tree partition indication information, the partitiondirection information, and the partition tree information may be entropyencoded/decoded. For the entropy-encoding/decoding of those types ofinformation, information on a neighboring coding unit adjacent to thecurrent coding unit may be used. For example, there is a highprobability that the partition type (the partitioned or non-partitioned,the partition tree, and/or the partition direction) of a leftneighboring coding unit and/or an upper neighboring coding unit of acurrent coding unit is similar to that of the current coding unit.Therefore, context information for entropy encoding/decoding of theinformation on the current coding unit may be derived from theinformation on the neighboring coding units. The information on theneighboring coding units may include at least any one of quad partitioninformation, multi-type tree partition indication information, partitiondirection information, and partition tree information.

As another example, among binary tree partitioning and ternary treepartitioning, binary tree partitioning may be preferentially performed.That is, a current coding unit may primarily undergo binary treepartitioning, and then a coding unit corresponding to a leaf node of abinary tree may be set as a root node for ternary tree partitioning. Inthis case, neither quad tree partitioning nor binary tree partitioningmay not be performed on the coding unit corresponding to a node of aternary tree.

A coding unit that cannot be partitioned by a quad tree partitionstructure, a binary tree partition structure, and/or a ternary treepartition structure becomes a basic unit for coding, prediction and/ortransformation. That is, the coding unit cannot be further partitionedfor prediction and/or transformation. Therefore, the partition structureinformation and the partition information used for partitioning a codingunit into prediction units and/or transformation units may not bepresent in a bit stream.

However, when the size of a coding unit (i.e., a basic unit forpartitioning) is larger than the size of a maximum transformation block,the coding unit may be recursively partitioned until the size of thecoding unit is reduced to be equal to or smaller than the size of themaximum transformation block. For example, when the size of a codingunit is 64×64 and when the size of a maximum transformation block is32×32, the coding unit may be partitioned into four 32×32 blocks fortransformation. For example, when the size of a coding unit is 32×64 andthe size of a maximum transformation block is 32×32, the coding unit maybe partitioned into two 32×32 blocks for the transformation. In thiscase, the partitioning of the coding unit for transformation is notsignaled separately, and may be determined through comparison betweenthe horizontal or vertical size of the coding unit and the horizontal orvertical size of the maximum transformation block. For example, when thehorizontal size (width) of the coding unit is larger than the horizontalsize (width) of the maximum transformation block, the coding unit may bevertically bisected. For example, when the vertical size (length) of thecoding unit is larger than the vertical size (length) of the maximumtransformation block, the coding unit may be horizontally bisected.

Information of the maximum and/or minimum size of the coding unit andinformation of the maximum and/or minimum size of the transformationblock may be signaled or determined at an upper level of the codingunit. The upper level may be, for example, a sequence level, a picturelevel, a slice level, a tile group level, a tile level, or the like. Forexample, the minimum size of the coding unit may be determined to be4×4. For example, the maximum size of the transformation block may bedetermined to be 64×64. For example, the minimum size of thetransformation block may be determined to be 4×4.

Information of the minimum size (quad tree minimum size) of a codingunit corresponding to a leaf node of a quad tree and/or information ofthe maximum depth (the maximum tree depth of a multi-type tree) from aroot node to a leaf node of the multi-type tree may be signaled ordetermined at an upper level of the coding unit. For example, the upperlevel may be a sequence level, a picture level, a slice level, a tilegroup level, a tile level, or the like. Information of the minimum sizeof a quad tree and/or information of the maximum depth of a multi-typetree may be signaled or determined for each of an intra slice and aninter slice.

Difference information between the size of a CTU and the maximum size ofa transformation block may be signaled or determined at an upper levelof the coding unit. For example, the upper level may be a sequencelevel, a picture level, a slice level, a tile group level, a tile level,or the like. Information of the maximum size of the coding unitscorresponding to the respective nodes of a binary tree (hereinafter,referred to as a maximum size of a binary tree) may be determined basedon the size of the coding tree unit and the difference information. Themaximum size of the coding units corresponding to the respective nodesof a ternary tree (hereinafter, referred to as a maximum size of aternary tree) may vary depending on the type of slice. For example, foran intra slice, the maximum size of a ternary tree may be 32×32. Forexample, for an inter slice, the maximum size of a ternary tree may be128×128. For example, the minimum size of the coding units correspondingto the respective nodes of a binary tree (hereinafter, referred to as aminimum size of a binary tree) and/or the minimum size of the codingunits corresponding to the respective nodes of a ternary tree(hereinafter, referred to as a minimum size of a ternary tree) may beset as the minimum size of a coding block.

As another example, the maximum size of a binary tree and/or the maximumsize of a ternary tree may be signaled or determined at the slice level.Alternatively, the minimum size of the binary tree and/or the minimumsize of the ternary tree may be signaled or determined at the slicelevel.

Depending on size and depth information of the above-described variousblocks, quad partition information, multi-type tree partition indicationinformation, partition tree information and/or partition directioninformation may be included or may not be included in a bit stream.

For example, when the size of the coding unit is not larger than theminimum size of a quad tree, the coding unit does not contain quadpartition information. Thus, the quad partition information may bededuced from a second value.

For example, when the sizes (horizontal and vertical sizes) of a codingunit corresponding to a node of a multi-type tree are larger than themaximum sizes (horizontal and vertical sizes) of a binary tree and/orthe maximum sizes (horizontal and vertical sizes) of a ternary tree, thecoding unit may not be binary-partitioned or ternary-partitioned.Accordingly, the multi-type tree partition indication information maynot be signaled but may be deduced from a second value.

Alternatively, when the sizes (horizontal and vertical sizes) of acoding unit corresponding to a node of a multi-type tree are the same asthe maximum sizes (horizontal and vertical sizes) of a binary treeand/or are two times as large as the maximum sizes (horizontal andvertical sizes) of a ternary tree, the coding unit may not be furtherbinary-partitioned or ternary-partitioned. Accordingly, the multi-typetree partition indication information may not be signaled but be derivedfrom a second value. This is because when a coding unit is partitionedby a binary tree partition structure and/or a ternary tree partitionstructure, a coding unit smaller than the minimum size of a binary treeand/or the minimum size of a ternary tree is generated.

Alternatively, the binary tree partitioning or the ternary treepartitioning may be limited on the basis of the size of a virtualpipeline data unit (hereinafter, a pipeline buffer size). For example,when the coding unit is divided into sub-coding units which do not fitthe pipeline buffer size by the binary tree partitioning or the ternarytree partitioning, the corresponding binary tree partitioning or ternarytree partitioning may be limited. The pipeline buffer size may be thesize of the maximum transform block (e.g., 64×64). For example, when thepipeline buffer size is 64×64, the division below may be limited.

-   -   N×M (N and/or M is 128) Ternary tree partitioning for coding        units    -   128×N (N<=64) Binary tree partitioning in horizontal direction        for coding units    -   N×128 (N<=64) Binary tree partitioning in vertical direction for        coding units

Alternatively, when the depth of a coding unit corresponding to a nodeof a multi-type tree is equal to the maximum depth of the multi-typetree, the coding unit may not be further binary-partitioned and/orternary-partitioned. Accordingly, the multi-type tree partitionindication information may not be signaled but may be deduced from asecond value.

Alternatively, only when at least one of vertical direction binary treepartitioning, horizontal direction binary tree partitioning, verticaldirection ternary tree partitioning, and horizontal direction ternarytree partitioning is possible for a coding unit corresponding to a nodeof a multi-type tree, the multi-type tree partition indicationinformation may be signaled. Otherwise, the coding unit may not bebinary-partitioned and/or ternary-partitioned. Accordingly, themulti-type tree partition indication information may not be signaled butmay be deduced from a second value.

Alternatively, only when both of the vertical direction binary treepartitioning and the horizontal direction binary tree partitioning orboth of the vertical direction ternary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingunit corresponding to a node of a multi-type tree, the partitiondirection information may be signaled. Otherwise, the partitiondirection information may not be signaled but may be derived from avalue indicating possible partitioning directions.

Alternatively, only when both of the vertical direction binary treepartitioning and the vertical direction ternary tree partitioning orboth of the horizontal direction binary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingtree corresponding to a node of a multi-type tree, the partition treeinformation may be signaled. Otherwise, the partition tree informationmay not be signaled but be deduced from a value indicating a possiblepartitioning tree structure.

FIG. 4 is a view showing an intra-prediction process.

Arrows from center to outside in FIG. 4 may represent predictiondirections of intra prediction modes.

Intra encoding and/or decoding may be performed by using a referencesample of a neighbor block of the current block. A neighbor block may bea reconstructed neighbor block. For example, intra encoding and/ordecoding may be performed by using an encoding parameter or a value of areference sample included in a reconstructed neighbor block.

A prediction block may mean a block generated by performing intraprediction. A prediction block may correspond to at least one among CU,PU and TU. A unit of a prediction block may have a size of one among CU,PU and TU. A prediction block may be a square block having a size of2×2, 4×4, 16×16, 32×32 or 64×64 etc. or may be a rectangular blockhaving a size of 2×8, 4×8, 2×16, 4×16 and 8×16 etc.

Intra prediction may be performed according to intra prediction mode forthe current block. The number of intra prediction modes which thecurrent block may have may be a fixed value and may be a valuedetermined differently according to an attribute of a prediction block.For example, an attribute of a prediction block may comprise a size of aprediction block and a shape of a prediction block, etc.

The number of intra-prediction modes may be fixed to N regardless of ablock size. Or, the number of intra prediction modes may be 3, 5, 9, 17,34, 35, 36, 65, or 67 etc. Alternatively, the number of intra-predictionmodes may vary according to a block size or a color component type orboth. For example, the number of intra prediction modes may varyaccording to whether the color component is a luma signal or a chromasignal. For example, as a block size becomes large, a number ofintra-prediction modes may increase. Alternatively, a number ofintra-prediction modes of a luma component block may be larger than anumber of intra-prediction modes of a chroma component block.

An intra-prediction mode may be a non-angular mode or an angular mode.The non-angular mode may be a DC mode or a planar mode, and the angularmode may be a prediction mode having a specific direction or angle. Theintra-prediction mode may be expressed by at least one of a mode number,a mode value, a mode numeral, a mode angle, and mode direction. A numberof intra-prediction modes may be M, which is larger than 1, includingthe non-angular and the angular mode. In order to intra-predict acurrent block, a step of determining whether or not samples included ina reconstructed neighbor block may be used as reference samples of thecurrent block may be performed. When a sample that is not usable as areference sample of the current block is present, a value obtained byduplicating or performing interpolation on at least one sample valueamong samples included in the reconstructed neighbor block or both maybe used to replace with a non-usable sample value of a sample, thus thereplaced sample value is used as a reference sample of the currentblock.

FIG. 7 is a diagram illustrating reference samples capable of being usedfor intra prediction.

As shown in FIG. 7, at least one of the reference sample line 0 to thereference sample line 3 may be used for intra prediction of the currentblock. In FIG. 7, the samples of a segment A and a segment F may bepadded with the samples closest to a segment B and a segment E,respectively, instead of retrieving from the reconstructed neighboringblock. Index information indicating the reference sample line to be usedfor intra prediction of the current block may be signaled. When theupper boundary of the current block is the boundary of the CTU, only thereference sample line 0 may be available. Therefore, in this case, theindex information may not be signaled. When a reference sample lineother than the reference sample line 0 is used, filtering for aprediction block, which will be described later, may not be performed.

When intra-predicting, a filter may be applied to at least one of areference sample and a prediction sample based on an intra-predictionmode and a current block size.

In case of a planar mode, when generating a prediction block of acurrent block, according to a position of a prediction target samplewithin a prediction block, a sample value of the prediction targetsample may be generated by using a weighted sum of an upper and leftside reference sample of a current sample, and a right upper side andleft lower side reference sample of the current block. In addition, incase of a DC mode, when generating a prediction block of a currentblock, an average value of upper side and left side reference samples ofthe current block may be used. In addition, in case of an angular mode,a prediction block may be generated by using an upper side, a left side,a right upper side, and/or a left lower side reference sample of thecurrent block. In order to generate a prediction sample value,interpolation of a real number unit may be performed.

In the case of intra prediction between color components, a predictionblock for the current block of the second color component may begenerated on the basis of the corresponding reconstructed block of thefirst color component. For example, the first color component may be aluma component, and the second color component may be a chromacomponent. For intra prediction between color components, the parametersof the linear model between the first color component and the secondcolor component may be derived on the basis of the template. Thetemplate may include upper and/or left neighboring samples of thecurrent block and upper and/or left neighboring samples of thereconstructed block of the first color component corresponding thereto.For example, the parameters of the linear model may be derived using asample value of a first color component having a maximum value amongsamples in a template and a sample value of a second color componentcorresponding thereto, and a sample value of a first color componenthaving a minimum value among samples in the template and a sample valueof a second color component corresponding thereto. When the parametersof the linear model are derived, a corresponding reconstructed block maybe applied to the linear model to generate a prediction block for thecurrent block. According to a video format, subsampling may be performedon the neighboring samples of the reconstructed block of the first colorcomponent and the corresponding reconstructed block. For example, whenone sample of the second color component corresponds to four samples ofthe first color component, four samples of the first color component maybe sub-sampled to compute one corresponding sample. In this case, theparameter derivation of the linear model and intra prediction betweencolor components may be performed on the basis of the correspondingsub-sampled samples. Whether or not to perform intra prediction betweencolor components and/or the range of the template may be signaled as theintra prediction mode.

The current block may be partitioned into two or four sub-blocks in thehorizontal or vertical direction. The partitioned sub-blocks may besequentially reconstructed. That is, the intra prediction may beperformed on the sub-block to generate the sub-prediction block. Inaddition, dequantization and/or inverse transform may be performed onthe sub-blocks to generate sub-residual blocks. A reconstructedsub-block may be generated by adding the sub-prediction block to thesub-residual block. The reconstructed sub-block may be used as areference sample for intra prediction of the sub-sub-blocks. Thesub-block may be a block including a predetermined number (for example,16) or more samples. Accordingly, for example, when the current block isan 8×4 block or a 4×8 block, the current block may be partitioned intotwo sub-blocks. Also, when the current block is a 4×4 block, the currentblock may not be partitioned into sub-blocks. When the current block hasother sizes, the current block may be partitioned into four sub-blocks.Information on whether or not to perform the intra prediction based onthe sub-blocks and/or the partitioning direction (horizontal orvertical) may be signaled. The intra prediction based on the sub-blocksmay be limited to be performed only when reference sample line 0 isused. When the intra prediction based on the sub-block is performed,filtering for the prediction block, which will be described later, maynot be performed.

The final prediction block may be generated by performing filtering onthe prediction block that is intra-predicted. The filtering may beperformed by applying predetermined weights to the filtering targetsample, the left reference sample, the upper reference sample, and/orthe upper left reference sample. The weight and/or the reference sample(range, position, etc.) used for the filtering may be determined on thebasis of at least one of a block size, an intra prediction mode, and aposition of the filtering target sample in the prediction block. Thefiltering may be performed only in the case of a predetermined intraprediction mode (e.g., DC, planar, vertical, horizontal, diagonal,and/or adjacent diagonal modes). The adjacent diagonal mode may be amode in which k is added to or subtracted from the diagonal mode. Forexample, k may be a positive integer of 8 or less.

An intra-prediction mode of a current block may be entropyencoded/decoded by predicting an intra-prediction mode of a blockpresent adjacent to the current block. When intra-prediction modes ofthe current block and the neighbor block are identical, information thatthe intra-prediction modes of the current block and the neighbor blockare identical may be signaled by using predetermined flag information.In addition, indicator information of an intra-prediction mode that isidentical to the intra-prediction mode of the current block amongintra-prediction modes of a plurality of neighbor blocks may besignaled. When intra-prediction modes of the current block and theneighbor block are different, intra-prediction mode information of thecurrent block may be entropy encoded/decoded by performing entropyencoding/decoding based on the intra-prediction mode of the neighborblock.

FIG. 5 is a diagram illustrating an embodiment of an inter predictionprocess.

In FIG. 5, a rectangle may represent a picture. In FIG. 5, an arrowrepresents a prediction direction. Pictures may be categorized intointra pictures (I pictures), predictive pictures (P pictures), andBi-predictive pictures (B pictures) according to the encoding typethereof.

The I picture may be encoded through intra-prediction without requiringinter prediction. The P picture may be encoded through inter predictionby using a reference picture that is present in one direction (i.e.,forward direction or backward direction) with respect to a currentblock. The B picture may be encoded through inter prediction by usingreference pictures that are preset in two directions (i.e., forwarddirection and backward direction) with respect to a current block. Whenthe inter prediction is used, the encoder may perform inter predictionor motion compensation and the decoder may perform the correspondingmotion compensation.

Hereinbelow, an embodiment of the inter prediction will be described indetail.

The inter prediction or motion compensation may be performed using areference picture and motion information.

Motion information of a current block may be derived during interprediction by each of the encoding apparatus 100 and the decodingapparatus 200. The motion information of the current block may bederived by using motion information of a reconstructed neighboringblock, motion information of a collocated block (also referred to as acol block or a co-located block), and/or a block adjacent to theco-located block. The co-located block may mean a block that is locatedspatially at the same position as the current block, within a previouslyreconstructed collocated picture (also referred to as a col picture or aco-located picture). The co-located picture may be one picture among oneor more reference pictures included in a reference picture list.

The derivation method of the motion information may be differentdepending on the prediction mode of the current block. For example, aprediction mode applied for inter prediction includes an AMVP mode, amerge mode, a skip mode, a merge mode with a motion vector difference, asubblock merge mode, a triangle partition mode, an inter-intracombination prediction mode, affine mode, and the like. Herein, themerge mode may be referred to as a motion merge mode.

For example, when the AMVP is used as the prediction mode, at least oneof motion vectors of the reconstructed neighboring blocks, motionvectors of the co-located blocks, motion vectors of blocks adjacent tothe co-located blocks, and a (0, 0) motion vector may be determined asmotion vector candidates for the current block, and a motion vectorcandidate list is generated by using the emotion vector candidates. Themotion vector candidate of the current block can be derived by using thegenerated motion vector candidate list. The motion information of thecurrent block may be determined based on the derived motion vectorcandidate. The motion vectors of the collocated blocks or the motionvectors of the blocks adjacent to the collocated blocks may be referredto as temporal motion vector candidates, and the motion vectors of thereconstructed neighboring blocks may be referred to as spatial motionvector candidates.

The encoding apparatus 100 may calculate a motion vector difference(MVD) between the motion vector of the current block and the motionvector candidate and may perform entropy encoding on the motion vectordifference (MVD). In addition, the encoding apparatus 100 may performentropy encoding on a motion vector candidate index and generate abitstream. The motion vector candidate index may indicate an optimummotion vector candidate among the motion vector candidates included inthe motion vector candidate list. The decoding apparatus may performentropy decoding on the motion vector candidate index included in thebitstream and may select a motion vector candidate of a decoding targetblock from among the motion vector candidates included in the motionvector candidate list by using the entropy-decoded motion vectorcandidate index. In addition, the decoding apparatus 200 may add theentropy-decoded MVD and the motion vector candidate extracted throughthe entropy decoding, thereby deriving the motion vector of the decodingtarget block.

Meanwhile, the coding apparatus 100 may perform entropy-coding onresolution information of the calculated MVD. The decoding apparatus 200may adjust the resolution of the entropy-decoded MVD using the MVDresolution information.

Meanwhile, the coding apparatus 100 calculates a motion vectordifference (MVD) between a motion vector and a motion vector candidatein the current block on the basis of an affine model, and performsentropy-coding on the MVD. The decoding apparatus 200 derives a motionvector on a per sub-block basis by deriving an affine control motionvector of a decoding target block through the sum of the entropy-decodedMVD and an affine control motion vector candidate.

The bitstream may include a reference picture index indicating areference picture. The reference picture index may be entropy-encoded bythe encoding apparatus 100 and then signaled as a bitstream to thedecoding apparatus 200. The decoding apparatus 200 may generate aprediction block of the decoding target block based on the derivedmotion vector and the reference picture index information.

Another example of the method of deriving the motion information of thecurrent may be the merge mode. The merge mode may mean a method ofmerging motion of a plurality of blocks. The merge mode may mean a modeof deriving the motion information of the current block from the motioninformation of the neighboring blocks. When the merge mode is applied,the merge candidate list may be generated using the motion informationof the reconstructed neighboring blocks and/or the motion information ofthe collocated blocks. The motion information may include at least oneof a motion vector, a reference picture index, and an inter predictionindicator. The prediction indicator may indicate one-directionprediction (L0 prediction or L1 prediction) or two-direction predictions(L0 prediction and L1 prediction).

The merge candidate list may be a list of motion information stored. Themotion information included in the merge candidate list may be at leastone of motion information (spatial merge candidate) of a neighboringblock adjacent to the current block, motion information (temporal mergecandidate) of the collocated block of the current block in the referencepicture, new motion information generated by a combination of the motioninformation existing in the merge candidate list, motion information(history-based merge candidate) of the block that is encoded/decodedbefore the current block, and zero merge candidate.

The encoding apparatus 100 may generate a bitstream by performingentropy encoding on at least one of a merge flag and a merge index andmay signal the bitstream to the decoding apparatus 200. The merge flagmay be information indicating whether or not to perform the merge modefor each block, and the merge index may be information indicating thatwhich neighboring block, among the neighboring blocks of the currentblock, is a merge target block. For example, the neighboring blocks ofthe current block may include a left neighboring block on the left sideof the current block, an upper neighboring block disposed above thecurrent block, and a temporal neighboring block temporally adjacent tothe current block.

Meanwhile, the coding apparatus 100 performs entropy-coding on thecorrection information for correcting the motion vector among the motioninformation of the merge candidate and signals the same to the decodingapparatus 200. The decoding apparatus 200 can correct the motion vectorof the merge candidate selected by the merge index on the basis of thecorrection information. Here, the correction information may include atleast one of information on whether or not to perform the correction,correction direction information, and correction size information. Asdescribed above, the prediction mode that corrects the motion vector ofthe merge candidate on the basis of the signaled correction informationmay be referred to as a merge mode having the motion vector difference.

The skip mode may be a mode in which the motion information of theneighboring block is applied to the current block as it is. When theskip mode is applied, the encoding apparatus 100 may perform entropyencoding on information of the fact that the motion information of whichblock is to be used as the motion information of the current block togenerate a bit stream, and may signal the bitstream to the decodingapparatus 200. The encoding apparatus 100 may not signal a syntaxelement regarding at least any one of the motion vector differenceinformation, the encoding block flag, and the transform coefficientlevel to the decoding apparatus 200.

The subblock merge mode may mean a mode that derives the motioninformation in units of sub-blocks of a coding block (CU). When thesubblock merge mode is applied, a subblock merge candidate list may begenerated using motion information (sub-block based temporal mergecandidate) of the sub-block collocated to the current sub-block in thereference image and/or an affine control point motion vector mergecandidate.

The triangle partition mode may mean a mode that derives motioninformation by partitioning the current block into diagonal directions,derives each prediction sample using each of the derived motioninformation, and derives the prediction sample of the current block byweighting each of the derived prediction samples.

The inter-intra combined prediction mode may mean a mode that derives aprediction sample of the current block by weighting a prediction samplegenerated by inter prediction and a prediction sample generated by intraprediction.

The decoding apparatus 200 may correct the derived motion information byitself. The decoding apparatus 200 may search the predetermined regionon the basis of the reference block indicated by the derived motioninformation and derive the motion information having the minimum SAD asthe corrected motion information.

The decoding apparatus 200 may compensate a prediction sample derivedvia inter prediction using an optical flow.

FIG. 6 is a diagram illustrating a transform and quantization process.

As illustrated in FIG. 6, a transform and/or quantization process isperformed on a residual signal to generate a quantized level signal. Theresidual signal is a difference between an original block and aprediction block (i.e., an intra prediction block or an inter predictionblock). The prediction block is a block generated through intraprediction or inter prediction. The transform may be a primarytransform, a secondary transform, or both. The primary transform of theresidual signal results in transform coefficients, and the secondarytransform of the transform coefficients results in secondary transformcoefficients.

At least one scheme selected from among various transform schemes whichare preliminarily defined is used to perform the primary transform. Forexample, examples of the predefined transform schemes include discretecosine transform (DCT), discrete sine transform (DST), andKarhunen-Loève transform (KLT). The transform coefficients generatedthrough the primary transform may undergo the secondary transform. Thetransform schemes used for the primary transform and/or the secondarytransform may be determined according to coding parameters of thecurrent block and/or neighboring blocks of the current block.Alternatively, transform information indicating the transform scheme maybe signaled. The DCT-based transform may include, for example, DCT-2,DCT-8, and the like. The DST-based transform may include, for example,DST-7.

A quantized-level signal (quantization coefficients) may be generated byperforming quantization on the residual signal or a result of performingthe primary transform and/or the secondary transform. The quantizedlevel signal may be scanned according to at least one of a diagonalup-right scan, a vertical scan, and a horizontal scan, depending on anintra prediction mode of a block or a block size/shape. For example, asthe coefficients are scanned in a diagonal up-right scan, thecoefficients in a block form change into a one-dimensional vector form.Aside from the diagonal up-right scan, the horizontal scan ofhorizontally scanning a two-dimensional block form of coefficients orthe vertical scan of vertically scanning a two-dimensional block form ofcoefficients may be used depending on the intra prediction mode and/orthe size of a transform block. The scanned quantized-level coefficientsmay be entropy-encoded to be inserted into a bitstream.

A decoder entropy-decodes the bitstream to obtain the quantized-levelcoefficients. The quantized-level coefficients may be arranged in atwo-dimensional block form through inverse scanning. For the inversescanning, at least one of a diagonal up-right scan, a vertical scan, anda horizontal scan may be used.

The quantized-level coefficients may then be dequantized, then besecondary-inverse-transformed as necessary, and finally beprimary-inverse-transformed as necessary to generate a reconstructedresidual signal.

Inverse mapping in a dynamic range may be performed for a luma componentreconstructed through intra prediction or inter prediction beforein-loop filtering. The dynamic range may be divided into 16 equal piecesand the mapping function for each piece may be signaled. The mappingfunction may be signaled at a slice level or a tile group level. Aninverse mapping function for performing the inverse mapping may bederived on the basis of the mapping function. In-loop filtering,reference picture storage, and motion compensation are performed in aninverse mapped region, and a prediction block generated through interprediction is converted into a mapped region via mapping using themapping function, and then used for generating the reconstructed block.However, since the intra prediction is performed in the mapped region,the prediction block generated via the intra prediction may be used forgenerating the reconstructed block without mapping/inverse mapping.

When the current block is a residual block of a chroma component, theresidual block may be converted into an inverse mapped region byperforming scaling on the chroma component of the mapped region. Theavailability of the scaling may be signaled at the slice level or thetile group level. The scaling may be applied only when the mapping forthe luma component is available and the division of the luma componentand the division of the chroma component follow the same tree structure.The scaling may be performed on the basis of an average of sample valuesof a luma prediction block corresponding to the color difference block.In this case, when the current block uses inter prediction, the lumaprediction block may mean a mapped luma prediction block. A valuenecessary for the scaling may be derived by referring to a lookup tableusing an index of a piece to which an average of sample values of a lumaprediction block belongs. Finally, by scaling the residual block usingthe derived value, the residual block may be switched to the inversemapped region. Then, chroma component block restoration, intraprediction, inter prediction, in-loop filtering, and reference picturestorage may be performed in the inverse mapped area.

Information indicating whether the mapping/inverse mapping of the lumacomponent and chroma component is available may be signaled through aset of sequence parameters.

The prediction block of the current block may be generated on the basisof a block vector indicating a displacement between the current blockand the reference block in the current picture. In this way, aprediction mode for generating a prediction block with reference to thecurrent picture is referred to as an intra block copy (IBC) mode. TheIBC mode may be applied to M×N (M<=64, N<=64) coding units. The IBC modemay include a skip mode, a merge mode, an AMVP mode, and the like. Inthe case of a skip mode or a merge mode, a merge candidate list isconstructed, and the merge index is signaled so that one merge candidatemay be specified. The block vector of the specified merge candidate maybe used as a block vector of the current block. The merge candidate listmay include at least one of a spatial candidate, a history-basedcandidate, a candidate based on an average of two candidates, and azero-merge candidate. In the case of an AMVP mode, the difference blockvector may be signaled. In addition, the prediction block vector may bederived from the left neighboring block and the upper neighboring blockof the current block. The index on which neighboring block to use may besignaled. The prediction block in the IBC mode is included in thecurrent CTU or the left CTU and limited to a block in the alreadyreconstructed area. For example, a value of the block vector may belimited such that the prediction block of the current block ispositioned in an area of three 64×64 blocks preceding the 64×64 block towhich the current block belongs in the coding/decoding order. Bylimiting the value of the block vector in this way, memory consumptionand device complexity according to the IBC mode implementation may bereduced.

Hereinafter, various embodiments of the present invention will bedescribed with reference to the drawings.

According to the present invention, prediction of split coding blocksmay be performed on the current coding block. Prediction of split codingblocks performed by the apparatus for encoding an image may include ablock partitioning step, a motion information derivation step, a motionestimation and compensation step, a motion information storage step,and/or an entropy encoding step. Prediction of split coding blocksperformed by the apparatus for decoding an image may include an entropydecoding step, a block partitioning step, a motion informationderivation step, a motion estimation and compensation step, and/or amotion information storage step.

In performing prediction of split coding blocks on the current codingblock, the block partitioning step may be performed. For example, thecurrent coding block may be subjected to block partitioning using atleast one method among quadrangular symmetric partitioning, triangularsymmetric partitioning, quadrangular asymmetric partitioning, andtriangular asymmetric partitioning. The split coding block may refer tothe basis of at least one among prediction, motion informationderivation, motion compensation, and motion information storage.Different methods may be applied to the bases. For example, in the casewhere the split coding block is the basis of prediction, prediction maybe performed by applying different methods to the split coding blocks.

FIG. 8 is a diagram illustrating an example of quadrangular symmetricpartitioning according to the present invention.

As shown in FIG. 8, quadrangular symmetric partitioning may be symmetricbinary partitioning. For example, the current coding block may besubjected to vertical symmetric binary partitioning as shown in FIG.8(a), or may be subjected to horizontal symmetric binary partitioning asshown in FIG. 8(b). The blocks generated as a result of the partitioningmay be the split coding blocks, respectively.

In the example of FIG. 8(a), the left split coding block may be referredto as a first split coding block, and the right split coding block maybe referred to as a second split coding block. However, without beinglimited thereto, the sequence of the split coding blocks may be changed.

Also, in FIG. 8(b), the upper split coding block may be referred to as afirst split coding block, and the lower split coding block may bereferred to as a second split coding block. However, without beinglimited thereto, the sequence of the split coding blocks may be changed.

FIG. 9 is a diagram illustrating an example of quadrangular quadpartitioning according to the present invention.

As shown in FIG. 9, quadrangular symmetric partitioning may be quadpartitioning. Quadrangular quad partitioning may refer to a method ofpartitioning a target block into four blocks by using a horizontal lineand a vertical line.

The current coding block may be partitioned into four split codingblocks as shown in FIGS. 9(a), 9(b), and 9(c). Each of the split codingblocks may be a prediction block. The split coding block may have apredetermined size (for example, 8×8 or 4×4). As shown in FIG. 9, thesplit coding blocks may be referred to as first to fourth split codingblocks, respectively. However, without being limited thereto, thesequence of the split coding blocks may be changed.

FIG. 10 is a diagram illustrating an example of triangular symmetricpartitioning according to the present invention.

As shown in FIG. 10, triangular symmetric partitioning (or diagonalpartitioning) may be performed on the current coding block.

The triangular symmetric partitioning may be triangular binarypartitioning. For example, the triangular binary partitioning may be topleft-bottom right diagonal symmetric binary partitioning as shown inFIG. 10(a). Alternatively, the triangular binary partitioning may be topright-bottom left diagonal symmetric binary partitioning as shown inFIG. 10(b). The blocks generated as a result of the triangular binarypartitioning may be referred to as the split coding blocks,respectively. When the shape of the current coding block is not a squareshape, the current coding block is partitioned as shown in FIGS. 10(c),10(d), 10(e), and 10(f). In the example shown in FIG. 10, the sequenceof a first split coding block and a second split coding block may bechanged.

FIG. 11 is a diagram illustrating an example of triangular quadpartitioning according to the present invention.

As shown in FIG. 11, triangular symmetric partitioning may be triangularquad partitioning. Triangular quad partitioning may refer to a method ofpartitioning a target block into four blocks by using a top left-bottomright diagonal and a top right-bottom left diagonal.

As shown in FIGS. 11(a) to 11(c), the encoding target block may bepartitioned into four blocks using two diagonals. The blocks generatedas a result of the partitioning may be referred to as the split codingblocks, respectively. The sequence of four split coding blocks may be asshown in FIG. 11. However, without being limited thereto, the sequenceof the first split coding block to the fourth split coding block may bechanged.

FIG. 12 is a diagram illustrating an example of quadrangular asymmetricpartitioning according to the present invention.

Quadrangular asymmetric partitioning may be performed on the currentcoding block. The quadrangular asymmetric partitioning may be asymmetricbinary partitioning. The asymmetric binary partitioning may be verticalasymmetric binary partitioning or horizontal asymmetric binarypartitioning. For example, the current coding block may be partitionedin the vertical or horizontal direction with an n:m ratio. Herein, n andm may be different positive integers.

For example, asymmetric binary partitioning may be 1:3 horizontalasymmetric binary partitioning as shown in FIG. 12(a). Alternatively,asymmetric binary partitioning may be horizontal asymmetric binarypartitioning having a ratio of at least one among 3:1, 2:3, and 3:2.

For example, asymmetric binary partitioning may be 1:3 verticalasymmetric binary partitioning as shown in FIG. 12(b). Alternatively,asymmetric binary partitioning may be vertical asymmetric binarypartitioning having a ratio of at least one among 3:1, 2:3, and 3:2.

In the example shown in FIG. 12, the sequence of a first split codingblock and a second split coding block that are generated as a result ofthe partitioning may be changed.

FIG. 13 is a diagram illustrating another example of quadrangularasymmetric partitioning according to the present invention.

As shown in FIG. 13, quadrangular asymmetric partitioning may beasymmetric ternary partitioning. The asymmetric ternary partitioning maybe vertical asymmetric ternary partitioning or horizontal asymmetricternary partitioning. The ratio of asymmetry may be n:m:n. Herein, n andm may be different positive integers. Alternatively, the ratio ofasymmetry may be 1:m:n. Herein, n and m may be different positiveintegers other than 1.

For example, asymmetric ternary partitioning may be 1:2:1 horizontalasymmetric ternary partitioning as shown in FIG. 13(a). Alternatively,asymmetric ternary partitioning may be 1:3:1 horizontal asymmetricternary partitioning.

For example, asymmetric ternary partitioning may be 1:2:1 verticalasymmetric ternary partitioning as shown in FIG. 13(b). Alternatively,asymmetric ternary partitioning may be 1:3:1 vertical asymmetric ternarypartitioning.

In the example shown in FIG. 13, the sequence of a first split codingblock to a third split coding block that are generated as a result ofthe partitioning may be changed.

FIG. 14 is a diagram illustrating an example of triangular asymmetricpartitioning according to the present invention.

Triangular asymmetric partitioning may be performed on the currentcoding block. The triangular asymmetric partitioning may be topleft-bottom right diagonal asymmetric binary partitioning or topright-bottom left diagonal asymmetric binary partitioning. For example,the top left-bottom right diagonal asymmetric binary partitioning may beas shown in FIG. 14(a) or 14(b). For example, the top right-bottom leftdiagonal asymmetric binary partitioning may be as shown in FIG. 14(c) or14(d).

In the example shown in FIG. 14, the sequence of a first split codingblock and a second split coding block that are generated as a result ofthe partitioning may be changed.

An angle at which partitioning is performed in the triangular asymmetricpartitioning may have a value ranging from 0 degrees to 180 degrees. Forexample, the angle at which partitioning is performed may be 45 degreesor 135 degrees.

A position (for example, a partitioning boundary) at which partitioningis performed in the triangular asymmetric partitioning may bedetermined. For example, it may be determined by deriving a horizontalor vertical length from the partitioning boundary to at least one amongthe top left, the top right, the bottom left, and the bottom right ofthe current block.

FIG. 15 is a diagram illustrating another example of triangularasymmetric partitioning according to the present invention.

As shown in FIG. 15, triangular asymmetric partitioning may be topleft-bottom right diagonal asymmetric ternary partitioning or topright-bottom left diagonal asymmetric ternary partitioning. For example,top left-bottom right diagonal asymmetric ternary partitioning may be asshown in FIG. 15(a). For example, top right-bottom left diagonalasymmetric ternary partitioning may be as shown in FIG. 15(b).

In the example shown in FIG. 15, the sequence of a first split codingblock to a third split coding block that are generated as a result ofthe partitioning may be changed.

An angle at which partitioning is performed in the triangular asymmetricpartitioning may have a value ranging from 0 degrees to 180 degrees. Forexample, the angle at which partitioning is performed may be 45 degreesor 135 degrees.

In the example shown in FIG. 15, the angle at which partitioning intothe first split coding block and the second split coding block isperformed and the angle at which partitioning into the second splitcoding block and the third split coding block may be different from eachother.

In performing prediction of split coding blocks on the current codingblock, the motion information derivation step may be performed.

The motion information derivation step may be performed using at leastone piece of inter prediction information among spatially neighboringmotion information, temporally neighboring motion information,combination motion information, and buffer-based motion information. Asingle motion information candidate list or multiple motion informationcandidate lists are constructed using the inter prediction informationso that motion information for the split coding blocks may be derived.

The spatially neighboring motion information may refer to availablemotion information of the neighboring block spatially adjacent to thecurrent block.

FIG. 16 is a diagram illustrating an example of spatially neighboringblocks of the current block.

In the example shown in FIG. 16, the spatially neighboring block may beat least one of blocks that are present at positions A to K. Forexample, the spatially neighboring blocks may be neighboring blockscorresponding to the positions A, B, F, J, and K.

The temporally neighboring motion information may refer to availablemotion information of the neighboring block temporally adjacent to thecurrent block.

FIG. 17 is a diagram illustrating an example of temporally neighboringblocks of the current block.

In the example shown in FIG. 17, the temporally neighboring block may beat least one of blocks that are present at positions L, M, N, and Oinside the previous picture in which encoding/decoding is completed. Theprevious picture in which encoding/decoding is completed may be apicture in the reference picture list. The previous picture includingthe temporally neighboring block may be the picture closest to thecurrent picture on the basis of POC (Picture Order Count).

The motion information may be stored in a buffer. For example, n piecesof motion information may be stored in the buffer, wherein n is apositive integer. The buffer-based motion information may refer tomotion information present in the buffer. The pieces of motioninformation of the target coding block may be stored in the bufferaccording to encoding order.

The motion information inside the buffer may be managed according to aparticular method. For example, when the buffer is full, the managementis performed with First In First Out (FIFO).

The combination motion information may be motion information generatedby combining the spatially neighboring motion information, thetemporally neighboring motion information, and the buffer-based motioninformation.

For example, in generating the combination motion information, one pieceof bi-directional motion information is selected among theabove-described pieces of the motion information and two pieces ofuni-directional motion information (L0 motion information and L1 motioninformation) that constitute the bi-directional motion information arecombined so that uni-directional motion information may be generated.

Alternatively, in generating the combination motion information, two ormore pieces of the motion information are selected among theabove-described pieces of the motion information and the selected two ormore pieces of the motion information are combined so that thecombination motion information may be generated.

Combining pieces of the motion information may refer to deriving anaverage or a weighted average of pieces of the uni-directional motioninformation.

For example, the combination motion information may be L0 directionmotion information generated by averaging motion information in which L1direction motion information of the selected bi-directional motioninformation is scaled in L0 direction and L0 direction motioninformation of the selected bi-directional motion information.

Alternatively, the combination motion information may be L1 directionmotion information generated by averaging motion information in which L0direction motion information of the selected bi-directional motioninformation is scaled in L1 direction and L1 direction motioninformation of the selected bi-directional motion information.

Alternatively, the combination motion information may be uni-directionalprediction information or bi-directional prediction information thatconsists of L0 direction motion information which is generated byaveraging pieces of L0 direction motion information of the selected twoor more pieces of motion information, and/or of L1 direction motioninformation which is generated by averaging pieces of L1 directionmotion information.

In order for the motion information to be available, 1) motioninformation is able to be referenced, and 2) the referenced motioninformation is different from the pieces of motion information presentin the motion information candidate list. Herein, in order to be able tobe referenced, memory access to the position of the referencedneighboring block needs to be possible, and motion information of theblock needs to be stored.

A case that motion information of any block is available may refer to acase that the motion information is motion information appropriate forthe motion information candidate list. For example, when the motioninformation candidate list is able to include only uni-directionalmotion information, bi-directional motion information is not available.Alternatively, for example, when the motion information candidate listis able to include only uni-directional motion information, theuni-directional motion information is derived on the basis of thebi-directional motion information. The derived uni-directional motioninformation may be included in the motion information candidate list asavailable motion information.

In performing the motion information derivation step on the currentcoding block, a single motion information candidate list may beconstructed. The single motion information candidate list may be onecandidate list having n pieces of motion information, wherein n is apositive integer. Herein, the motion information may be bi-directionalmotion information and/or uni-directional motion information of thespatially neighboring motion information, the temporally neighboringmotion information, the combination motion information, and/or thebuffer-based motion information. The single motion information candidatelist may be used in common for various prediction modes for deriving themotion information by using the motion information candidate list.

The single motion information candidate list may include n pieces ofbi-directional motion information and of uni-directional motioninformation, wherein n is a positive integer. In order to fill thesingle motion information candidate list, searching may be performedwith respect to multiple neighboring blocks. When available motioninformation is found, the motion information is included in the singlemotion information candidate list. The search process may be as follows.

For example, the single motion information candidate list may have fivecandidates, and the single motion information candidate list may befilled with the motion information of the spatially neighboring block,the motion information of the temporally neighboring block, thecombination motion information, the buffer-based motion information, andzero motion information in that order.

The spatially neighboring blocks may be searched in J→B→K→A→F order, andup to four available motion information candidates may be derived. Thetemporally neighboring blocks may be searched in O→L order, or up to oneavailable motion information candidate may be derived from one among Oand L. With respect to each of the combination motion information, thebuffer-based motion information, and the zero motion information, up tofive available candidates may be derived.

When the spatially neighboring block or the temporally neighboring blockcorresponds to a predetermined mode, it is determined that motioninformation of the neighboring block is unavailable motion information.For example, the predetermined mode may be at least one of interprediction modes or a CPR (Current Picture Referencing) mode.

When the spatially neighboring block or the temporally neighboring blockdeviates from the boundary of at least one among a CTU, a tile, a slice,and a picture, it is determined that motion information of the block isunavailable motion information.

The single motion information candidate list may include n pieces ofuni-directional motion information, wherein n is a positive integer.Searching for filling the single motion information candidate list isperformed. When motion information is available, L0 or L1uni-directional motion information of the motion information is includedin the single motion information candidate list.

For example, the L0 uni-directional motion information may be includedin a predetermined index in the single motion information candidatelist. Further, the L1 uni-directional motion information may be includedin another predetermined index in the single motion informationcandidate list. Herein, when a reconstructed index is the predeterminedindex, it is determined that this indicates L0 prediction. When areconstructed index is the other predetermined index, it is determinedthat this indicates L1 prediction.

For example, when the single motion information candidate list includessix candidates, the L0 uni-directional motion information is included inindexes 0, 1, and 2, and the L1 uni-directional motion information isincluded in indexes 3, 4, and 5. Herein, when the reconstructed index is0, 1, or 2, it is determined that this indicates L0 prediction. When thereconstructed index is 3, 4, or 5, it is determined that this indicatesL1 prediction.

For example, when the single motion information candidate list includesfive candidates, the L0 uni-directional motion information is includedin indexes 0, 1, and 2, and the L1 uni-directional motion information isincluded in indexes 3 and 4. Herein, when the reconstructed index is 0,1, or 2, it is determined that this indicates L0 prediction. When thereconstructed index is 3 or 4, it is determined that this indicates L1prediction.

For example, the L0 uni-directional motion information may be includedin the even number index in the single motion information candidate listand the L1 uni-directional motion information may be included in the oddnumber index. Herein, when the reconstructed index is an even number, itis determined that this indicates L0 prediction. When the reconstructedindex is an odd number, it is determined that this indicates L1prediction.

For example, the L1 uni-directional motion information may be includedin the even number index in the single motion information candidate listand the L0 uni-directional motion information may be included in the oddnumber index. Herein, when the reconstructed index is an even number, itis determined that this indicates L1 prediction. When the reconstructedindex is an odd number, it is determined that this indicates L0prediction.

For example, the L1 uni-directional motion information may be includedin a predetermined index in the single motion information candidatelist. Further, the L0 uni-directional motion information may be includedin another predetermined index in the single motion informationcandidate list. Herein, when a reconstructed index is the predeterminedindex, it is determined that this indicates L1 prediction. When areconstructed index is the other predetermined index, it is determinedthat this indicates L0 prediction.

The prediction direction of the motion information indicated by thereconstructed index and the prediction direction determined by thereconstructed index may be the same or differ. When the predictiondirection of the motion information indicated by the reconstructed indexand the prediction direction determined by the reconstructed index arethe same, the determined prediction direction is maintained. When theprediction direction of the motion information indicated by thereconstructed index and the prediction direction determined by thereconstructed index differ, the determined prediction direction ischanged. For example, the prediction direction determined to be L0prediction may be changed to L1 prediction.

Alternatively, when the motion information indicated by thereconstructed index includes the motion information in the predictiondirection determined by the reconstructed index, the determinedprediction direction is maintained. When the motion informationindicated by the reconstructed index does not include the motioninformation in the prediction direction determined by the reconstructedindex, the determined prediction direction is changed.

The above-described prediction direction may be information indicatingwhether the reference picture list including the reference picture is anL0 list or an L1 list. In this specification, the prediction directionand a reference picture direction may be used as having the samemeaning.

A search process for constructing the candidate list may be performed ontemporally/spatially neighboring uni-directional (L0 or L1) motioninformation (J→B→K→A→F→O→L), uni-directional motion information oftemporally/spatially neighboring bi-directional motion information,combined uni-directional motion information using temporally/spatiallyneighboring bi-directional motion information, and the zero motioninformation in that order. The motion information derived through thesearch process may be included in the single motion informationcandidate list. The search order may be changed.

The motion information of the split coding blocks may be derived fromthe single motion information list.

Pieces of the motion information of multiple split coding blocks may bederived using different indexes.

For example, when there are five candidates in the single motioninformation candidate list and there are two split coding blocks, motioninformation of a first split coding block is selected as one of the fivecandidates and motion information of a second split coding block isselected as one of the four candidates except the selected candidate.The index indicating one of five candidates may be encoded/decoded. Forexample, the index of the first split coding block and the index of thesecond split coding block have different values to indicate differentcandidates. When the index of the decoded first split coding block andthe index of the decoded second split coding block have the same value,the value of the index of the second split coding block is increased by1 and the modified index is used as the final index of the second splitcoding block.

Alternatively, pieces of motion information of multiple split codingblocks may be derived using different index regions.

For example, when there are six candidates in the single motioninformation candidate list and there are two split coding blocks, afirst index region of the single motion information candidate list isindexes 0, 1, and 2, and a second index region is indexes 3, 4, and 5.Herein, the motion information of the first split coding block may be,for example, selected as one of candidates corresponding to the indexesincluded in the first index region. Further, the motion information ofthe second split coding block may be, for example, selected as one ofcandidates corresponding to the indexes included in the second indexregion.

In deriving the motion information for the current coding block,multiple motion information candidate lists may be constructed. themultiple motion information candidate lists may be m candidate listsincluding n pieces of motion information as candidates, wherein m is apositive integer and n is a positive integer. Herein, the motioninformation may be at least one among the spatially neighboring motioninformation, the temporally neighboring motion information, thecombination motion information, and the bi-directional motioninformation or the uni-directional motion information of thebuffer-based motion information.

The number of the multiple motion information candidate lists may be thesame as the number of the split coding blocks. Further, referencedirections of the motion information of the multiple motion informationcandidate lists may vary with each candidate list.

For example, when the number of the multiple motion informationcandidate lists is 2, a first motion information candidate list consistsof L0 uni-directional motion information. Further, a second motioninformation candidate list may consist of L1 uni-directional motioninformation.

For example, when the number of the multiple motion informationcandidate lists is 3, the first motion information candidate listconsists of L0 uni-directional motion information. Further, the secondmotion information candidate list may consist of bi-directional motioninformation. Further, a third motion information candidate list mayconsist of L1 uni-directional motion information candidate.

For example, when the number of the multiple motion informationcandidate lists is 3, the first motion information candidate list andthe second motion information candidate list consist of bi-directionalmotion information. Further, the third motion information candidate listmay consist of L0 uni-directional motion information.

When there are multiple motion information candidate lists, the motioninformation of the split coding blocks is derived from a designatedmotion information candidate list.

For example, when there are two split coding blocks and there are twomotion information candidate lists, the motion information of a firstsplit coding block is derived from a first motion information candidatelist. Further, the motion information of a second split coding block maybe derived from a second motion information candidate list.

Pieces of motion information of the multiple split coding blocks may bederived from different motion information candidate lists.

A method of constructing multiple motion information candidate lists maybe the same as a method of constructing a single motion informationcandidate list.

In performing prediction of split coding blocks on the current codingblock, the motion estimation and motion compensation step may beperformed.

The motion estimation and motion compensation step may be performedusing at least one among uni-directional prediction, bi-directionalprediction, weighted bi-directional prediction, prediction of splitblocks, partitioning boundary smoothing, and intra prediction.

The motion information used in motion estimation and motion compensationmay be at least one among a motion vector, reference direction and areference picture index.

When uni-directional prediction is performed, L0 direction motioninformation or L1 direction motion information is used. When the motionvector of the uni-directional motion information is based on a subpixel,a prediction block based on the subpixel is generated through subpixelinterpolation.

When bi-directional prediction is performed, L0 direction motioninformation and L1 direction motion information within bi-directionalmotion information are used. Herein, two results of uni-directionalmotion estimation are averaged to generate a bi-directional predictionblock. Each of the two uni-directional predictions when bi-directionalprediction is performed may be the same as the above-describeduni-directional prediction.

When weighted bi-directional prediction is performed, L0 directionmotion information and L1 direction motion information withinbi-directional motion information are used. Herein, two results ofuni-directional motion estimation are averaged in a weighted manner togenerate a bi-directional prediction block. For example, a weightingfactor of 3/8 is applied to the result of L0 direction motion estimationand a weighting factor of 5/8 is applied to the result of L1 directionmotion estimation, and the results are added. Alternatively, forexample, a weighting factor of 3/4 is applied to the result of L0direction motion estimation and a weighting factor of 1/4 is applied tothe result of L1 direction motion estimation, and the results are added.

When prediction of split blocks is performed, motion information thateach split coding block has is used to generate a prediction block forthe split coding block. Herein, the prediction block of each splitcoding block may be generated by uni-directional prediction orbi-directional prediction.

FIG. 18 is a diagram illustrating prediction of split blocks accordingto the present invention.

For example, as shown in FIG. 18(a), the current coding block may besubjected to top left-bottom right diagonal symmetric binarypartitioning. Herein, motion information of a first split coding blockmay be used to perform first partitioning prediction on thecorresponding region. Further, motion information of a second splitcoding block may be used to perform second partitioning prediction onthe corresponding region.

For example, as shown in FIG. 18(b), the current coding block may besubjected to top right-bottom left diagonal symmetric binarypartitioning. Herein, motion information of a first split coding blockmay be used to perform first partitioning prediction on thecorresponding region. Further, motion information of a second splitcoding block may be used to perform second partitioning prediction onthe corresponding region.

In the example shown in FIG. 18, the sequence of the first partitioningprediction and the second partitioning prediction may be changed.

When prediction of split blocks is performed on the current codingblock, motion information of each split coding block is used to generatea prediction block for the current coding block. Herein, the predictionblock may be generated by uni-directional prediction or bi-directionalprediction. Afterward, a pre-defined weighting factor may be used toperform a weighted sum on a per-sample basis. Herein, weighting factorsbased on samples may be predefined differently according to a block sizeand/or block partitioning information.

FIG. 19 is a diagram illustrating an example of weighting factors basedon samples which are used for a weighted sum for prediction of splitblocks.

For example, in the case where the size of the current coding block is8×8 and where the current coding block is subjected to top left-bottomright diagonal symmetric binary partitioning, prediction for the currentcoding block using motion information of a first split coding block maybe first prediction and prediction for the current coding block usingmotion information of a second split coding block may be secondprediction. The weighting factors shown in FIG. 19(a) may be applied tothe first prediction. Further, the weighting factors shown in FIG. 19(b)may be applied to the second prediction.

For example, the weighting factors may vary with each pixel.

When the partitioning boundary smoothing is performed, a splitprediction block for the current block is generated and then smoothingis performed on the block boundary.

When prediction of split blocks is performed on the current codingblock, motion information of each split coding block is used to generatea prediction block for the current coding block and the pre-definedweighting factors are used to perform a weighted sum on a per-samplebasis. Herein, weighting factors based on samples may be predefineddifferently according to a block size and/or block partitioninginformation.

For example, weighting factors may be {7/8, 6/8, 5/8, 4/8, 3/8, 2/8,1/8} with boundary samples in the center.

For example, weighting factors may be {1/8, 2/8, 3/8, 4/8, 5/8, 6/8,7/8} with boundary samples in the center.

For example, weighting factors may be {7/8, 6/8, 4/8, 2/8, 1/8} withboundary samples in the center.

For example, weighting factors may be {1/8, 2/8, 4/8, 6/8, 7/8} withboundary samples in the center.

For example, weighting factors may be {7/8, 4/8, 1/8} with boundarysamples in the center.

For example, weighting factors may be {1/8, 4/8, 7/8} with boundarysamples in the center.

For example, weighting factors may be {6/8, 4/8, 2/8} with boundarysamples in the center.

For example, weighting factors may be {2/8, 4/8, 6/4} with boundarysamples in the center.

Herein, the boundary samples may be samples corresponding to theboundary between the split blocks.

FIG. 20 is a diagram illustrating an example of boundary samples ofsplit blocks.

In FIG. 20, samples in a dark gray color are boundary samples.Specifically, FIG. 20(a) shows an example of boundary samples fordiagonal binary partitioning, and FIG. 20(b) shows an example ofboundary samples for diagonal ternary partitioning.

FIG. 21 is a diagram illustrating weighting factors applied to boundarysamples.

For example, in the case where the size of the current coding block is8×8 and where the current coding block is subjected to top left-bottomright diagonal symmetric binary partitioning, prediction for the currentcoding block using motion information of a first split coding block maybe first prediction and prediction for the current coding block usingmotion information of a second split coding block may be secondprediction. The weighting factors shown in FIG. 21(a) may be applied tothe first prediction. Further, the weighting factors shown in FIG. 21(b)may be applied to the second prediction.

In performing prediction of split coding blocks on the current codingblock, the motion information storage step may be performed.

The motion information storage step may be performed using at least onemethod among integrated-motion information storage and split-blockmotion information storage.

The motion information may be stored on a per-n×n size basis. The motioninformation may be stored in a motion information buffer for temporallyneighboring blocks and may be used in search of spatially neighboringblocks. The expression n may have a value of at least one among 2, 4, 8,16, 32, 64, 128, and 256.

FIG. 22 is a diagram illustrating the basis of storage of motioninformation.

In the case where the size of the current coding block is 16×16 and thebasis of storage of the motion information is 4×4, the motioninformation may be stored as shown in FIG. 22.

When the integrated-motion information storage is performed, one pieceof motion information is stored for the current coding block region.Herein, the integrated motion information may be bi-directional motioninformation or uni-directional motion information.

The integrated motion information may be derived from pieces of motioninformation of multiple split coding blocks.

For example, in the case where the current coding block consists of twosplit coding blocks and where pieces of motion information of therespective split coding blocks are uni-directional motion informationand are also motion information in different directions, one piece ofbi-directional motion information that consists of two pieces of motioninformation may be generated.

For example, in the case where the current coding block consists of twosplit coding blocks and where pieces of motion information of therespective split coding blocks are uni-directional motion informationand are also motion information in the same direction, one piece ofbi-directional motion information that consists of motion information inwhich one of the two pieces of uni-directional motion information isscaled into motion information in the opposite direction, and of theother uni-directional motion information may be generated.

The scaling may be scaling L0 uni-directional motion information into L1uni-directional motion information or scaling L1 uni-directional motioninformation into L0 uni-directional motion information. Herein, when thereference picture of the target motion information is the same as thereference picture in the opposite direction, the target motioninformation is converted into the motion information in the oppositedirection without performing scaling.

For example, in the case where the current coding block consists of twosplit coding blocks and where pieces of motion information of therespective split coding blocks are uni-directional motion informationand are also motion information in the same direction, the integratedmotion information may be motion information of a first split codingblock or motion information of a second split coding block.

For example, in the case where the current coding block consists ofmultiple split coding blocks and where pieces of motion information ofthe respective split coding blocks are uni-directional motioninformation and are also motion information in the same direction,multiple pieces of motion information may be averaged to generate onepiece of uni-directional motion information.

For example, in the case where the current coding block consists ofmultiple split coding blocks and where pieces of motion information ofthe respective split coding blocks are uni-directional motioninformation and bi-directional motion information, pieces of motioninformation corresponding to the respective directions may be averagedto generate two pieces of uni-directional motion information and onepiece of bi-directional motion information which consists of thegenerated two pieces of uni-directional motion information may begenerated.

For example, in the case where the current coding block consists ofmultiple split coding blocks and where pieces of motion information ofthe respective split coding blocks are uni-directional motioninformation and bi-directional motion information, pieces of motioninformation corresponding to the respective directions may be averagedin a weighted manner to generate two pieces of uni-directional motioninformation and one piece of bi-directional motion information whichconsists of the generated two pieces of uni-directional motioninformation may be generated.

When the split-block motion information storage is performed, motioninformation of each split coding block is used to store motioninformation for the corresponding region.

Herein, the motion information of each split coding block may bebi-directional motion information or uni-directional motion information.With respect to the region corresponding to the boundary between thesplit coding blocks, integrated motion information derived from motioninformation of split coding blocks adjacent to the boundary may bestored.

FIG. 23 is a diagram illustrating an example of split-block motioninformation storage according to the present invention.

In the case where the size of the current coding block is 16×16 and inthe case of top left-bottom right diagonal symmetric binarypartitioning, motion information may be stored as shown in FIG. 23. Inthe example of FIG. 23, first motion information may be motioninformation of a first split coding block and second motion informationmay be motion information of a second split coding block. Further,integrated motion information may be motion information generated usingthe above-described method of generating the integrated motioninformation.

In the example shown in FIG. 23, integrated motion information for a 4×4block corresponding to the boundary between the split coding blocks maybe stored as first motion information of the first split coding block.Alternatively, integrated motion information for the block correspondingto the boundary may be stored as second motion information of the secondsplit coding block.

In the example shown in FIG. 23, integrated motion information for a 4×4block corresponding to the boundary between the split coding blocks maybe stored using the first motion information of the first split codingblock and the second motion information of the second split codingblock. For example, in the case where a reference picture direction ofthe first motion information is the same as a reference picturedirection of the second motion information, first motion information orthe second motion information may be stored as motion information of ablock corresponding to the boundary. For example, in the case where boththe reference picture of the first motion information and the referencepicture of the second motion information are L0 uni-directional, thesecond motion information of the second split coding block may be storedas motion information of a block corresponding to the boundary.Similarly, in the case where both the reference picture of the firstmotion information and the reference picture of the second motioninformation are L1 uni-directional, the second motion information of thesecond split coding block may be stored as motion information of a blockcorresponding to the boundary. Alternatively, the first motioninformation of the first split coding block may be stored as motioninformation of a block corresponding to the boundary.

For example, in the case where the reference picture direction of thefirst motion information and the reference picture direction of thesecond motion information differ, bi-directional motion information thatconsists of the first motion information and the second motioninformation may be stored as motion information of a block correspondingto the boundary.

In performing prediction of split coding blocks on the current codingblock, the entropy encoding and decoding step may be performed.

In the entropy encoding and decoding step, entropy encoding and decodingmay be performed on at least one among a partitioning predictionencoding operation flag, a partitioning direction, the number of splitblocks, index information of a motion information candidate list, andindex information of motion information.

Entropy encoding and decoding may include binarization of information,CABAC encoding, and/or bypass encoding.

The partitioning prediction encoding operation flag (triangular_flag)may indicate whether partitioning encoding prediction is performed onthe current coding block. When MMVD_flag, GBi_flag, orMH_intrainter_flag is 1, encoding and decoding of triangular_flag isomitted. Alternatively, triangular_flag may explicitly have a value of0.

The partitioning direction may indicate a top left-bottom right diagonaldirection or a top right-bottom left diagonal direction. For example,when a syntax (split_dir_flag) value for the partitioning direction is0, it refers to a top left-bottom right diagonal direction, and when thesyntax value is 1, it refers to a top right-bottom left diagonaldirection. Alternatively, when the syntax value is 1, it refers to a topleft-bottom right diagonal direction, and when the syntax value is 0, itrefers to a top right-bottom left diagonal direction.

The syntax (split_num_idx) regarding the number of split blocks mayrefer to one among binary partitioning prediction, ternary partitioningprediction, and/or quad partitioning prediction.

The syntax (split_cand_list_idx) regarding the index information of themotion information candidate list may indicate which list of multiplemotion information candidate list is used.

The syntax (cand_idx) regarding the index information of the motioninformation may indicate which piece of motion information among piecesof motion information included in the candidate list is used.

When prediction of split coding blocks is performed, binarization andencoding/decoding are performed on index information of pre-definedpossible combinations. The number of pre-defined combinations may beN×M×L× . . . . Herein, N may be the number of partitioning directions, Mmay be the number of motion information candidates that are possiblyassigned to the first split coding block, and L may be the number ofmotion information candidates that are possibly assigned to the secondsplit coding block.

For example, when the number of pre-defined possible combinations is 40(2×5×4), binarization and encoding/decoding are performed on indexinformation of the combinations.

For example, when the number of pre-defined possible combinations is 36(2×6×3), binarization and encoding/decoding are performed on indexinformation of the combinations.

For example, one motion information candidate list may have fourcandidates, and two thereof may be L0 motion information and theremaining two may be L1 motion information. Herein, when there are twosplit coding blocks, a first split coding block uses one of the fourcandidates and a second split coding block uses one of the twocandidates. Accordingly, the number of pre-defined possible combinationsmay be 16 (2×4×2), and binarization and encoding/decoding may beperformed on index information of the combinations. The binarization andthe encoding/decoding may be performed on the basis of probability ofthe 16 combinations.

The number of the pre-defined possible combinations may be limited to Nwhich is a particular positive integer.

For example, when there are 40 possible combinations, binarization andencoding/decoding are performed on index information corresponding tothe top 16 combinations of the combinations. Herein, the encodingapparatus and the decoding apparatus may not perform prediction on thecombinations except the top 16 combinations.

The binarization may be performed using at least one among MPM,exponential-Golomb coding, truncated unary binary coding, fixed lengthbinary coding, and truncated binary coding.

FIG. 24 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 40.

When the number of pre-defined possible combinations is 40, binarizationis performed as shown in FIGS. 24(a) and 24 (b).

FIG. 25 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 36.

When the number of pre-defined possible combinations is 36, binarizationis performed as shown in FIG. 25.

FIG. 26 is a diagram illustrating a binarization method when the numberof pre-defined combinations is 16.

When the number of pre-defined possible combinations is 16, binarizationis performed as shown in FIGS. 26(a) to 26(d).

Prediction of triangular split blocks is a technique in which thequadrangular current coding block is partitioned into two triangles onthe basis of a diagonal and each of the triangular split blocksresulting from the partitioning is subjected to inter prediction. Wheninter prediction is performed in triangular partitioning prediction,only uni-directional inter prediction is performed on each of thetriangular split blocks to solve a problem of memory access bandwidthincrease. The encoding apparatus may construct a motion information listfor the current coding block in order to derive motion information ofthe triangular split block, may use various combinations of partitioningdirections and pieces of the motion information to form a predictionblock, and may compare rate-distortion costs to find the optimumcombination.

Further, the motion information used in encoding of the current codingblock may be stored on a per-storage block basis, wherein the storageblock is of a particular size (4×4). When triangular partitioningprediction is performed on the current coding block, bi-directionalprediction motion information in which pieces of motion information(uni-directional prediction) of two triangular split blocks are combinedis stored for a block corresponding to regions that overlap, with theboundary between the two triangular split blocks in the center. Herein,when prediction directions of two pieces of motion information of thetwo triangular split blocks are the same, additional processing isrequired to generate bi-directional prediction information.

Therefore, it is limited in such a manner that the uni-directionalprediction in different directions is performed on two triangular splitblocks. That is, 1) the encoding apparatus performing prediction oftriangular split blocks may reduce the number of possible combinationsof a partitioning direction to be searched and of motion information ofeach triangular split block. Accordingly, the complexity of the encodingapparatus performing prediction of split coding blocks may be reduced,and overheads of bits for signaling the reduced number of combinationsmay be reduced. Further, 2) in the motion information storage process,pieces of motion information of the two triangular split blocksresulting from the partitioning are combined into motion information indifferent directions. Therefore, when motion information is stored,additional processing for generating bi-directional motion informationto be stored for the region corresponding to the boundary between thetwo triangular split blocks is unnecessary.

The above embodiments may be performed in the same method in an encoderand a decoder.

At least one or a combination of the above embodiments may be used toencode/decode a video.

A sequence of applying to above embodiment may be different between anencoder and a decoder, or the sequence applying to above embodiment maybe the same in the encoder and the decoder.

The above embodiment may be performed on each luma signal and chromasignal, or the above embodiment may be identically performed on luma andchroma signals.

A block form to which the above embodiments of the present invention areapplied may have a square form or a non-square form.

The above embodiment of the present invention may be applied dependingon a size of at least one of a coding block, a prediction block, atransform block, a block, a current block, a coding unit, a predictionunit, a transform unit, a unit, and a current unit. Herein, the size maybe defined as a minimum size or maximum size or both so that the aboveembodiments are applied, or may be defined as a fixed size to which theabove embodiment is applied. In addition, in the above embodiments, afirst embodiment may be applied to a first size, and a second embodimentmay be applied to a second size. In other words, the above embodimentsmay be applied in combination depending on a size. In addition, theabove embodiments may be applied when a size is equal to or greater thata minimum size and equal to or smaller than a maximum size. In otherwords, the above embodiments may be applied when a block size isincluded within a certain range.

For example, the above embodiments may be applied when a size of currentblock is 8×8 or greater. For example, the above embodiments may beapplied when a size of current block is 4×4 only. For example, the aboveembodiments may be applied when a size of current block is 16×16 orsmaller. For example, the above embodiments may be applied when a sizeof current block is equal to or greater than 16×16 and equal to orsmaller than 64×64.

The above embodiments of the present invention may be applied dependingon a temporal layer. In order to identify a temporal layer to which theabove embodiments may be applied, a corresponding identifier may besignaled, and the above embodiments may be applied to a specifiedtemporal layer identified by the corresponding identifier. Herein, theidentifier may be defined as the lowest layer or the highest layer orboth to which the above embodiment may be applied, or may be defined toindicate a specific layer to which the embodiment is applied. Inaddition, a fixed temporal layer to which the embodiment is applied maybe defined.

For example, the above embodiments may be applied when a temporal layerof a current image is the lowest layer. For example, the aboveembodiments may be applied when a temporal layer identifier of a currentimage is 1. For example, the above embodiments may be applied when atemporal layer of a current image is the highest layer.

A slice type or a tile group type to which the above embodiments of thepresent invention are applied may be defined, and the above embodimentsmay be applied depending on the corresponding slice type or tile grouptype.

In the above-described embodiments, the methods are described based onthe flowcharts with a series of steps or units, but the presentinvention is not limited to the order of the steps, and rather, somesteps may be performed simultaneously or in different order with othersteps. In addition, it should be appreciated by one of ordinary skill inthe art that the steps in the flowcharts do not exclude each other andthat other steps may be added to the flowcharts or some of the steps maybe deleted from the flowcharts without influencing the scope of thepresent invention.

The embodiments include various aspects of examples. All possiblecombinations for various aspects may not be described, but those skilledin the art will be able to recognize different combinations.Accordingly, the present invention may include all replacements,modifications, and changes within the scope of the claims.

The embodiments of the present invention may be implemented in a form ofprogram instructions, which are executable by various computercomponents, and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include stand-alone or acombination of program instructions, data files, data structures, etc.The program instructions recorded in the computer-readable recordingmedium may be specially designed and constructed for the presentinvention, or well-known to a person of ordinary skilled in computersoftware technology field. Examples of the computer-readable recordingmedium include magnetic recording media such as hard disks, floppydisks, and magnetic tapes; optical data storage media such as CD-RCMs orDVD-RCMs; magneto-optimum media such as floptical disks; and hardwaredevices, such as read-only memory (RCM), random-access memory (RAM),flash memory, etc., which are particularly structured to store andimplement the program instruction. Examples of the program instructionsinclude not only a mechanical language code formatted by a compiler butalso a high level language code that may be implemented by a computerusing an interpreter. The hardware devices may be configured to beoperated by one or more software modules or vice versa to conduct theprocesses according to the present invention.

Although the present invention has been described in terms of specificitems such as detailed elements as well as the limited embodiments andthe drawings, they are only provided to help more general understandingof the invention, and the present invention is not limited to the aboveembodiments. It will be appreciated by those skilled in the art to whichthe present invention pertains that various modifications and changesmay be made from the above description.

Therefore, the spirit of the present invention shall not be limited tothe above-described embodiments, and the entire scope of the appendedclaims and their equivalents will fall within the scope and spirit ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention may be used to encode or decode an image.

What is claimed is:
 1. A method of decoding an image, the methodcomprising: constructing a motion information list for a current block;reconstructing a first index for a first triangular block within thecurrent block and a second index for a second triangular block withinthe current block; and predicting the first triangular block and thesecond triangular block, based on the first index, the second index, andthe motion information list.
 2. The method of claim 1, wherein thecurrent block is a quadrangle, and the first triangular block and thesecond triangular block are regions that are generated by partitioningthe current block with a top left-bottom right diagonal or a topright-bottom left diagonal.
 3. The method of claim 2, whereininformation on whether the current block is partitioned with the topleft-bottom right diagonal or the top right-bottom left diagonal isdecoded from a bitstream.
 4. The method of claim 1, wherein the motioninformation list comprises a predetermined number of pieces of motioninformation in an order of motion information of a spatially neighboringblock, motion information of a temporally neighboring block,buffer-based motion information, combination motion information, andzero motion information.
 5. The method of claim 1, wherein the firstindex and the second index are different from each other.
 6. The methodof claim 1, wherein based on whether the first index or the second indexis a predetermined index, a prediction direction of the first triangularblock or the second triangular block is determined.
 7. The method ofclaim 6, wherein when the first index or the second index is an evennumber index, the prediction direction of the first triangular block orthe second triangular block is an L0 direction, and when the first indexor the second index is an odd number index, the prediction direction ofthe first triangular block or the second triangular block is an L1direction.
 8. The method of claim 6, wherein when motion informationindicated by the first index or the second index does not include motioninformation in the determined prediction direction, the determinedprediction direction is changed into the opposite direction.
 9. Themethod of claim 1, further comprising: storing motion information withinthe current block in a 4×4 block unit.
 10. The method of claim 9,wherein motion information of the second triangular block is stored asmotion information of a block corresponding to a boundary between thefirst triangular block and the second triangular block.
 11. A method ofencoding an image, the method comprising: determining motion informationfor a first triangular block within a current block and motioninformation for a second triangular block within the current block;predicting the first triangular block and the second triangular block,based on the motion information for the first triangular block and themotion information for the second triangular block; constructing amotion information list for the current block; and encoding a firstindex for the first triangular block and a second index for the secondtriangular block, based on the motion information for the firsttriangular block, the motion information for the second triangular blockand the motion information list.
 12. The method of claim 11, wherein thecurrent block is a quadrangle, and the first triangular block and thesecond triangular block are regions that are generated by partitioningthe current block with a top left-bottom right diagonal or a topright-bottom left diagonal.
 13. The method of claim 12, whereininformation on whether the current block is partitioned with the topleft-bottom right diagonal or the top right-bottom left diagonal isencoded into a bitstream.
 14. The method of claim 11, wherein the motioninformation list comprises a predetermined number of pieces of motioninformation in an order of motion information of a spatially neighboringblock, motion information of a temporally neighboring block,buffer-based motion information, combination motion information, andzero motion information.
 15. The method of claim 11, wherein the firstindex and the second index are different from each other.
 16. The methodof claim 11, wherein based on whether the first index or the secondindex is a predetermined index, a prediction direction of the firsttriangular block or the second triangular block is determined.
 17. Themethod of claim 16, wherein when the first index or the second index isan even number index, the prediction direction of the first triangularblock or the second triangular block is an L0 direction, and when thefirst index or the second index is an odd number index, the predictiondirection of the first triangular block or the second triangular blockis an L1 direction.
 18. The method of claim 16, wherein when motioninformation indicated by the first index or the second index does notinclude motion information in the determined prediction direction, thedetermined prediction direction is changed into the opposite direction.19. The method of claim 11, further comprising: storing motioninformation within the current block in a 4×4 block unit, wherein motioninformation of the second triangular block is stored as motioninformation of a block corresponding to a boundary between the firsttriangular block and the second triangular block.
 20. Acomputer-readable recording medium storing a bitstream that is received,decoded and used to reconstruct an image by an image decoding apparatus,the bitstream comprises a first index for a first triangular blockwithin a current block and a second index for a second triangular blockwithin the current block, the first index and the second index are usedwith a motion information list for the current block to predict thefirst triangular block and the second triangular block.